I always beat Tetris.

Yeah, that too. I'll probably never complete some of the harder games i have...even when i like them x)
But they're mostly action/arcade games and are supposed to be hard anyway ^^

Super Meat Boy

I guess you could say I always beat the Meat

To me FPS and RTS games usually seem to be designed easily beatable, and they are also easy to get back to even after a long hiatus. The only reason I wouldn't beat one is either due to boredom, or the game being too hard. I think Rise of Nations is too hard for me (on the hardest difficulty at least :)), simply because of that inane 90 minute time limit.

With many RPGs, I'd probably restart the game from the scratch after a long hiatus. That happened with e.g. Baldur's Gate, I probably restarted it five times before finally playing it till the end. A good quest log and automap help overcoming this, though. No need to restart if you can tell easily what were you in the process of doing before.

Point'n'click adventures are easy to beat... if I use a walkthrough. I'm unsure whether I've beaten any p'n'c adventure game without using a walkthrough at least occasionally, at some point I just get fed up wandering around without any idea what I should be doing next, inventory full of items with no idea where they should be used.

Then I check a walkthrough, and I realize there was some small hotspot I missed in one screen somewhere, or that naturally the needle needs to be used with the dead cat in order to unlock the car door. Doh!

The only adventure games I've probably beaten without using a proper walkthrough at all were probably the original ADVENT, and King's Quest (the first one), just because there were no online walkthroughs back then. However, even with them I changed hints with e.g. my friends or siblings, who were playing the same game. "Hey did you know you can push the rock, and under it you will find a cave with a dragon?". So even them I didn't really beat fully on my own.

Wait a minute, The Black Cauldron! I think I did beat it by myself, but it was an adventure game aimed at kids, with easier puzzles.

I play practically anything except for simulators and sports games. My most "mainstream" genres are RPG, real time strategy, shooters, arcades, beat em ups, sandbox.

But i actually bothered to finish completely all games i ever came across from a single specific genre i love, only; Shooter (or no shooter) horror. I have a very special soft spot for games like FEAR series, the Suffering series, Resident Evil 4, Manhunt 1 and 2, Call of Cthulhu Dark Corners of the Earth and others like them. This is the only genre i ever afforded to beat any game it falls in its category and it happened to be owned (or pirated) by me.