Recommend me a fun game to play

THPS2 woot. Not the PC port.

I find Starcraft 2 is my favorite, if you like RTS games I would definitely recommend this one. It happens to have a f2p version that lets you try out one team and a few maps if you are interested.

Saints Row The Third and Just Cause 2:)

From the games you already own, I highly recommend Rayman Origins if you like 2D-Platformers. Really charming with great art.

maybe these 08INT-EWP5Y-6T6XH , 04MCM-WKHEW-2KAJ9

Super { Meat Box - Hexagon}, your choice.

From smaller games: Bastion, Trine 1 & 2, Magicka, Orcs Must Die!, House of the Dead Ninjas and maybe Cave Story.

From bigger: Overlord 1 & 2, Max Payne 1 & 2, Saints Row 2 & 3, Serious Sam 3 and HD of First and Second Encounter and Portal 1 & 2.

Also try changing FOV maybe that would help.

Just Cause 2, Saints Row the Third, Dragon Age: Origins, Knights of the Old Republic, Mass Effect.

LoL as a moba suggestion. Smite probably will give you motion sickness like it did to me
Can't really help you with the other genres though

I saw that you have NightSky in your account, just completed it a few minutes ago, it's a great ambient physics game that get's quite challenging after a while.
Play it!

I noticed that you own Terraria but have never played it. I think that would be worth giving a try. It's a lot like minecraft except it's more about exploring around a limited map and finding all sorts of fantastical weapons. If you can find some sort of multiplayer server you can get even more fun out of it.

Edit: Oh, also Spec Ops - The Line. If you don't like third person shooters the game might feel really boring for the first hour or so, but if you stick with it the story is really good.

My Favoirte Games That I Still Play:
Saints Row The Third
Mafia 2
Postal 2
Warframe
Counter Strike Global Offensive

Maybe give yourseld a 1 month brake from gaming.

The Gothic series if you have't played it yet (especially 1 and 2) - amazing set and feel, addicting as hell and not as stiff as bethesda/bioware RPGs.

Some cool games that you haven't played:

1. Terraria is a cool adventure/survival game;
2. SimCity 4 if you like city building games;
3. Hitman Absolution if you like stealth games;
4. Batman: AA is an amazing adventure/stealth game;

If you have money, you should try Just Cause 2.