I have no idea why, but I started wondering...
What genres of games do people always beat?

Personally, I've never failed to complete games in the following genres:
- FPS (despite always playing the hardest difficulty)
- action-RPG
- JRPG (this is probably more patience than skill)
- tactics RPG
- Metroidvania
- action platformer (i.e. Cave Story)

And then there are the genres I never complete:
- point-and-click
- SHMUP (despite loving them anyway)
- traditional Roguelikes(Nethack, DCSS, etc.)
- RTS
- puzzle
- Zelda-likes (except for Link's Awakening)
- rhythm (I'm a musician, but that doesn't seem to help...)
- arena fighter


Perhaps I only beat the games that are designed for everyone to beat... I don't know. What do other people always beat?

I don't have any genre I always complete as it depends on the game.
But here are the ones I beat more often than others.

- FPS (they are short and fast-paced)
- RPGs
- RTS (though I don't know how you would evaluate when you beat one)
- Point and Click
- Visual Novels
- Tycoon simulators

RTS, FPS. and Dungeon Crawlers are pretty much it, but never on a high difficulty.

There aren't any genres that I always beat. I beat games if they manage to hold my interest which includes having an interesting story, an exciting world to explore and/or not being excruciatingly hard and frustrating. Most of those games are RPGs, story-telling FPS and point and click adventures, some are platformers.

I think I've never beaten any strategy, business sim or sports title, because they don't manage to hold my interest for long enough. I've beaten one or two Diablo-like action RPGs and I've come quite close to completion in others, but I often tend to lose interest in games of this genre somewhere along the way, too, if they're just about hacking, slashing and looting endlessly.

RPGs

Any game that is a collection fest feeds my OCD, so I usually complete those. The LEGO games are my kryptonite.

How do you beat a sim? Don't they just keep going?

All of them except adventures, although it's mostly their fault, since most of the puzzles are so fucking retarded .

RPG's I tend to always beat.

I'm an completionist, so I tend to finish every game I play, even the bad ones.
I don't play very often RTS, rogue-like, sims, FPS or survival simulators.

They usually have single player campaigns, I'm counting those.

There are genres that always beat me, does that count?

Yeah, you're right. I didn't think about that.

Really not a genre issue for me. I beat games from any genre but also never complete others from any genre.
I'm guessing it has to do with how involved i am in the game and how much fun i'm getting out of it.