Early Access (14) -Yeah, I got quite a few of these. You can say I'm part of the problem with bad Early Access games if you want, but I make sure to only buy the ones that are really doing well, such as 7 Days to Die, Subnautica, and Space Engineers.
FPS (78) - I got A LOT of these. I love first person shooters, or rather, the first person perspective. I love being able to get a much richer feel for an environment which I only can in first person rather than third. Plus, I usually enjoy more immersive, fast paced games, which first person shooters also deliver.
Horror (6) - I own a few games that technically qualify as horror, but I didn't put them in because I don't find them scary at all, such as Resident Evil. This mostly consists of Alien: Isolation and Amensia as the two better games in this category.
Indie (14) - These mostly came from Humble Bundle steam keys. A couple, such as Wrack, I actually bought directly from Steam.
Online Shooters (29) - This combines my love of first person shooters with my enjoyment of playing with friends/brother. Not all of them are first person online shooters, but most of them are.
Other Online (11) - As a result of above, I don't play many online only games that aren't shooters. This is what this category is for, for games like Torchlight II and Pool Nation.
Racing (9) - Pretty standard stuff here. I enjoy a good racing title now and then.
RPG/Adventure (29) - This is probably my most vague category. This includes games from Skyrim, to Assassin's Creed, to Nekopara and Guilty Gear. At some point I'll probably divide this into more accurate catagories, such as fighting, exploration, etc., but not until I own more of them in the first place.
Simulation (16) - A couple of these actually overlap into Other Online, but are necessarily online only, such as Civ 5. Others include ARMA, Euro Truck Simulator, and Tabletop Simulator.
Third Person Shooter (39) - Also pretty vague. Like mentioned before, this include Resident Evil, even the recent remaster game. Just don't find them scary enough to put in Horror. Other than that however, this is pretty standard with games like Saints Row The Third, Sleeping Dogs, GTA4, and Dead Rising.
Games (4) -This is just a throwaway category far at the bottom. I use this for junk like demos, unwanted betas, and those free trial games.