This thread is reserved for the title's purpose. Just list your favorite. I am gonna order mine, you dont have to. You can also explain why you picked them if you want.
Global Agenda: Free Agent - This was a game I picked up in 2010 when it was released through Steam for free. I loved it, giving up all my other games at that time. An entire summer was spent on it. There is not really anything like it that I know of. It is similar to World of Warcraft being and MMORPG, but it is much more. I stopped playing it and went back to it in 2013 and found it was pretty much dead. It can be revived though considering its status of being free.
Crysis Series (specifically Crysis 1/Warhead) - This game took me by surprise. Back in 2007 when I barely had a gaming computer (dualcore fx 62 and radeon 6900xt) at its time it can be considered acceptable. Anywho, I was walking through Target near Christmas and found two games that I thought looked cool but didnt know anything about one being Modern Warfare and the other being Crysis. I ended up asking my parents for both of them but only got Crysis from them, getting MW from someone else. The point is Crysis is unlike anything I had played and is still a classic of its time. It was beyond its time in graphics and an enormous sandbox playground. I had issues playing it with high detail, even to this day I average 60 fps with a 280x. This game will never be forgotten by myself. It's story is also compelling and almost theatrical like even though it is sandbox. Possibly a movie?
Half-Life Series (In its Entirety) - This should be placed in at second, but I am giving props to Crytek for blowing my mind and never having played a game of theirs in the past. I only heard of the original Far Cry game after I got Crysis (yes my world is extremely closed). To the point, Valve does an amazing job with story telling and detailed graphics. The story is so freaking good JJ Abrams my scifi bud might possibly adapt it to the big screen. This being announced a few years back.
Counter-Strike Series (In its Entirety) - The series has not changed excluding graphical updates. Well not noticeable changes. Every generation adds new weapons and changes the weapon menu up a bit. Nothing to gripe about. I have played since 1.6 before CSS and man was I a squeaker. I started around 8 - 9 years of age (2000 AD) when my older brother (by 10 years) played HL and CS and Delta Force and all them other goodies. Each graphical boost is much obliged. I must say the newest iteration of GO with skins just adds to the enjoyment.
Temple Run - The guys at Imanji or whatever they are called made one hell of an addictive game. Yes it is a mobile device based game, but in the car or sitting in a lobby I am likely to be found playing this game. It is a very basic game with few inputs (swiping and motion control via the device).
FEAR Series (FEAR's 1 and 2 exclude 3) - I am excluding the third because I havent played it yet. FEAR is a horror based first person shooter where you work for a secret government organization known as FEAR. Your mission is simple hunt down supernatural forces and prevent them from harming the planet. Anyways it scarred the crud out of me. It is a big install (both) being about 30gb between the first two including the expansions.
FIFA Series - I love all them FIFA games. Graphics get better, game play remains the same. It is like that with new iterations usually. I own it for PC and not console. So their shows you how special the PC Master race is, I went out and bought a HDE wireless adapter for the 360 controllers (was less than 10 bucks).
Killing Floor - I haven't played KF 2 yet, but the original is hellafun. Play by yourself or in CO-OP with friends or pubbers. It is by far the best zombie game to date for straight action. Not much story to it unlike Resident evil or even L4D campaign. It has a slew of DLC, weapons, character skins, etc. making it all the better from a great former indie dev.
Bugdom - I haven't played this in years, not since school that is. 1999 - 2009 (k-8), the Macs at my school had some pretty fun games including Gizmos and Gadgets, Bugdom, Nanosaur, Cromag Rally, and various other notable ones. Anyways the one that I enjoyed more than anything was Bugdom. I just loved being a pillbug or whatever you were avoiding giant walking human feet. There are clearly other obstacles aswell.
Pokemon (pretty all prior to 2006) - Considering I havent played any new ones I am just gonna say the classics are classics for a reason. They are playable for hours on end on a small as fucking screen. Now a days I rock a emulator for android and have since I had my first smartphone. It is by far the best classic game in mobile terms.
What are yours and why? I would like to know. :)