Terraria is my favorite game ever. I liked the Thorium mod that added musical instruments as weapons, as well as the gelatinous cube in the dungeon.
Skyrim is probably my 2nd favorite. It is horribly glitchy with most mods in my experience. I’ve been playing without mods recently.
Mount&Blade Warband is definitely on up there. I like the Perisno Mod the best, but I mess around with a lot of different mods on that game. I’m currently trying Prophecy of Pendor again, but it is stupidly slow to start and I’ll probably switch to a different mod pretty quickly.
In case you could not tell: I like mods and being able to customize my games 
I’m also a fan of turn-based games like Civilization (4 and 5), Endless Space (more 1 than 2), Fallen Enchantress, and XCOM (number 2 out of 3, I guess?).
I also have quite a few real-time strategies such as Sins of A Solar Empire, Star Wars Empire at War, Empire Earth, Age of Empires 2, etc.
Honorable Mentions: Fallout New Vegas, Star Wars Jedi Knight Jedi Academy, The Force Unleashed, Mass Effect (All 3 of course), Star Wars Battlefront 2 (the old one, I have it on PC as well as ye olde xbox). I’m generally not a fan of first person shooters unless it is heavily story integrated (Mass Effect) or star wars themed.
Also other ARPGs, such as Grim Dawn, POE (mostly with a nephew), and Torchlight 2 (I’ve never played 1). I usually play these the least (including D2R, for that matter). I don’t mind slow and grindy (mount and blade), I don’t mind difficult or slow, but something about the RNG of these types of games entertains me the least 
Of course, these are just the ones currently installed on my current computers, so this would be what I’ve played in the past year or two. I own a whole lot more
and this does not count any of the games I have only on console or have not played recently. I would probably list out about a hundred if I included all the older games I still enjoy going back and playing through from back in the day.