Quite often these are related. The reason I find it so hard to learn combos in fighting games, or figure out what I am supposed to do in Master of Orion or Civilization, might be at least partly because I don't see much point to really learn them. Sometimes I still try, though.

Not sure if the OP's original examples were either of games he/she really can't play at all, or doesn't just want to (learn to play them). I don't e.g. find stealth games that hard, in fact the stealth levels in Thief Gold tend to be much easier than the levels where you have to fight (e.g. against undeads, burricks etc.).

Lolwut, Civ games are practically automated, you could probably play through a game just by clicking of "Recommended" research without even understanding what's going on

For me, it's racing/driving games: I am horrendous at them. The only two I ever had success at were the old Grand Prix (because I cheated and took the shortcut through the box area everytime) and the Carmageddons, because there I was actually *supposed* to crash violently into things. It also diminishes my enjoyment (though not completely) of a big chunk of sandbox games, like Saints Row or GTA.
I can drive reasonably well in real life, though.

I can't say that I CAN'T play them, these are just games I don't prefer to play if I have something better. I try them out, especially if they're highly acclaimed, and then when I feel I've gotten the point, I skip out on them.

Early 3D games (I think rtcvb32 mentioned these already): Even back then I totally skipped out on those games (was way more into catching up with the adventure games that I had missed) because I just thought that they looked absolutely horrible. I try not to be such a superficial person, but the idea that my foot goes into a wall really irked me :D. Even now, for the older 3D games that everyone kept harping on about, I play it with extreme texture packs and such (still have to finish Deus Ex).

Tower Defense Games: Just not interested. Similarly, just not interested in MOBAs. Just not my thing.

"Indie Puzzle Platformer": I played a few of them when they were newer (Braid, Rochard, etc.), even enjoyed some, but there's such a glut of them now, I've just gotten totally tired of them now, and it is an automatic skip for me if I see a game labelled as such.

Horror games: I'm still willing to try this out if I find something worthy, but so far I haven't. I loved adventure games, but the horror ones at worst bored me (and never scared me) or at best I enjoyed them for their other characteristics. With stuff like Amnesia too I got bored of the mechanics pretty early in the game. Not sure Doom 3 counts, but the ridiculous jumpscares and the gun/torch swapping really annoyed me.

Grand Strategy games (I think stuff like Civ comes under this?)- I play them on occasion (especially if my friends are insisting), but the barrier to entry for me is too high, and the mechanics enjoyment is too slow coming, and they rarely have an interesting story for you to be engrossed in.

Oh, and not sure if it counts as a genre, but any time-dependent or non-puzzle game on a mobile device. I still haven't come around to the mindset that you can have a "serious" game on the phone, and the ones that try to be so don't really pull me, and I end up leaving them.

So you haven't played a civ game from civ 2 onwards? I still desperately want to play civ 2 some day, but I've been playing almost religiously from civ 3 onwards (played the first a buttload as well). I'd like to recommend Civ IV which I'm tempted to say is the best one in the series, and definitely I think easier to get into than the original, mostly because the original's interface is almost unbearably archaic at this point. I'm not too sure about it being the best seeing as how Civ V is brilliant as well, only they went kind of haywire with the religion aspect, I miss corporations, and the one unit per tile limit, although an improvement, needs to be tweaked some more.
One of the things that is so great about Civ IV, which I for some reason stupidly avoided like the plague for a long time, is the collection of scenarios. Basically it is the Civ experience condensed (not that it takes any less time to complete) to some particular timeframe or setting where you don't have to worry about tech trees and advancing through the technological ages fast enough. For example, one scenario the entire map is only the north eastern part of Africa and a bit of Asia where you fight for resources and trade revenue, while others only another only focus on the campaigns of Genghis Khan / Alexander the Great, and yet another one only focuses on some conflict in medieval Europe. There is also an awesome scenario about viking raids on the British Isles and western Europe, a cool one about colonial times in America, a brilliant historic one set in Japan, a ridiculously complex one about WW2 and at least one weird highly acclaimed sci-fi one. Of course there are also scenarios set in ancient Rome and Greece, which are perhaps my favorites.
Civ V also has some very good scenarios, and last time I checked there was even one where you could play as the Boers / Zulus in South Africa, which was awesome!

MMOs - I don't like playing games with other people.
Multiplayer shooters - Really, I'd just prefer to play single-player games.
MOBAs - Okay, fine, I don't mind playing boardgames with other people, but just not video games.

For me, it's totally WW2 shooters. I HATE, i mean H.A.T.E. them, to the point that i would not even play them if they were gifted. Then, games like SIMS. And last but not least, BASKET, FOOTBALL, sports games in general.

I hate those so much... Maybe because they are the closest thing a game can get to real life, modern or otherwise, which i really don't like the least bit.

DRM games makes me nervous, all those questions about blood type, shoe size and sexual preference followed by phone call to some exotic country.

MMO's in general.

Stealth games of the "Do or Die" sort ("You were spotted - Game Over") or any that don't offer you appropriate means for defense, flight or hiding if you're caught. Especially if paired with cruel checkpoint system.

"Hardcore" platformers - by which I don't necessarily mean games like VVVVVV or Super Meat Boy (although they might come close in concept), but the kind of games that pride themselves in a lack of save features and have you replay whole long levels if you die. The longer the levels and times without saving, the less able I am to endure these games (hence why hardcore "coffee break" games like VVVVVV and SMB can still be excused).

Pure strategy and business sim games - as they require the patience to study all their complicated rules and options before really getting into them, or to learn by making mistakes and having to start over. They also require a lot of time, and due to my personal preferences (imagination over figures, story over competition, exploration and audiovisual experience over challenge etc.) that time quickly feels wasted to me when spent with building, fighting, managing money only to win - just not rewarding enough (more like work without payment or learning something I'm not that interested in without actually having a use for it).

MMOs - as I need to know the game will be over in a manageable time, instead of artificially wasting mine with filler stuff, and I'm not all that keen to team up with random strangers for multiplayer games.

(I do admit though that many RPGs - one of my favorite genres - also feature some of the mentioned things I dislike in strategy games, business sims and MMOs, but in smaller quantities and while offering enough of what I enjoy to counteract them at the same time.)

And regarding the themes: more or less realistic military war games. I don't get anything out of their settings, I don't have a taste for military discipline, heroism, nationalism etc., it even digusts me in RL and these games are too close to reality for me to enjoy, and too bleak and boring for playing out fantasies.

I can play sports games, but I do it even less often than trying to play strategy games, because I'm not that interested in sports.

Of course, all of the above are extremes, and there are exceptions to any rule.

This thread is right up my street!

In terms of genres, I am awful at any strategy or tactical combat games. Also, any combat games involving a vehicle including sci-fi space battles. I can play puzzle games but don't have the patience, so I guess that's another genre that I'm useless at.

If I may wind the question out, I can't play ANY games that are generally considered difficult. Before buying a game I'll always google to check how hard it is. If they're too hard but still tempting, my next step is to see if there are any god mode cheats.

I usually avoid the ordinary base building units mass producing RTS games because they just bore me to death. The same goes for grindy diablo clones. I do make exceptions ofcourse. I played through Van Helsing not too long ago because it actually wasn't very grindy and it was short :D.

Racing: I really detest the thought of driving around in a circle and being able to call oneself a winner, like how the hell can there be progress if you wind up back where you started?

Only 2 racing games I ever like were PURE which was an ATV off road tricky style game that I regret selling. And Need for Speed Underground because it just played right and had an open world .

Sports: I'll watch Hockey and Football at the bar but that's it. I cant name more than 3 players and I'm sick of pretending I can. Fuck sports and fuck EA while were at it.

RTS's:
I loved C&C and Red Alert back in the day (even Dune) though I wasn't very good at them. That has not changed lol.

You really don't like playing with other people, do you? :)

No worries, I feel the same things. Too many times did you try some "popular" game and then shortly after I come our with a bitter taste in my mouth. Bad things about multiplayer: 1. Hard to interrupt if real life calls, 2. too many annoying people on the internet (this forum excluded of course), 3. often there is no proper feel of completion of the game - it just goes on until you are bored. 4. If it is competitive I will always remain a noob since I am bored of the game way before I get any good at it. And training in a guild requires way to much real world coordination.

Real-time strategy games. I lack the requisite timing or practicality or something, because I get brutally slaughtered even in early levels. It's embarrassing how bad I am at them, honestly. I can only hope none of you are ever trapped in a burning building with me if my instincts in that situation are anything like the ones that kick in when I start playing an RTS.

Hm, in that case I guess my answer should have been "all console games that were not released on PC, PS or PS2 and can't be emulated on the PC", just because I wouldn't own the required hardware. In theory, I can *play* games in any genre, I just don't manage to have fun with all of them, or to bring up enough energy to try and beat them regardless. ;)

Or if it's about sucking at certain game mechanics - I do suck big time in everything involving timed trials, and especially if it also involves precision racing/jumping/shooting etc.