I can't decide on actual ranks, so just my 10 favorite games from this generatin:
Arkham Asylum
Arkham City
(This Space Reserved for Arkham Origins...having watched that 30 demo, I'm positive I'm going to love it)
Mass Effect 1
Mass Effect 3 (I would say ME2, buuuuuuut as much as I like the series, I've liked other games more than the 2nd installment)
Oblivion
Skyrim
Bioshock
Bioshock Infinite
And Left 4 Dead 2.
Now, since i'm allowed to condense entire series into one slot...
(Edited to add in explinations)
Arkham Series
What's there to say? Easily the best set of Batman games ever made. The combat flows perfectly and when you get good at it by getting good at counters and throwing in some gadgets every now and then, it really captures the feel of what it'd be like to be Batman fighting 10 guys at once. I thought the stories have been fun in a comic-booky kind of way, and lets face it: the best part about the Batman series is the villains that he's up against, and these games are full of all the big names.
Mass Effect Series
Easily my favorite series of this generation. I remember beating the first game and thinking it was amazing...then I heard it was going to be a trilogy...then I heard that said trilogy is going to have save files carry over from one game to the next. At that point I started bouncing giddily like Liara after finding a new Prothean digsite. At the end of ME3, when all the squadmates are saying "This could be it, so I just wanted to say goodbye", it felt like they were breaking the fourth wall and saying goodbye to me (yeah, I'm a dork, I know)...but I had spent so much time with these characters...so many hours, so many playthroughs...I got very emotional due to all the goodbyes as it really finally sank in "This is it...the end to the saga".
Elder Scrolls Series
What's there to say? Perhaps the greatest first-person RPG series ever made. Bethesda releases buggy-ass games, but god damn are they good at story telling. It's what I like to call an A.D.D. RPG because TES will make you feel like you've got A.D.D. like nothing else will. "Well I'm supposed to be going over here to save some guy from a castle...but wait! That mage's guild quest is nearby! I want to explore those ruins! Look over there! A dragon's nest! Gonna go get me a soul and a new shout! But wait, the Assassin's Guild quest is in that town overthere and those quests are ALWAYS fun! You start the game with a clear purpose: Gonna go save the Empire (or in Skyrim's case, "Gonna go save the province!") but as soon as you're out of the gate the game tells you "Alright, go have fun. We don't mind how, just know that there IS a main questline somewhere around here, but don't let that distract you from the countless other distractions in this game."
Bioshock Series
Great stories, great characters, great gameplay. Not much else I can say about it. :3
Darksiders Series
Having never played a God of War game, I had to settle for these "Like God of War but..." games. And sorry, but I did get swept up in the whole "You're one of the Four Hoursemen" business...that alone makes the games badass if you ask me.
Left 4 Dead series
Mindless fun running through zombies with three of your close buddies. Plenty of zombie head explosions and a pretty decent challenge if you're not a sissy and play on the difficulties above Normarl.
Portal Series
Easily the best set of puzzle games I've ever played. So unique and interesting...many of the puzzles have actually rather simple solutions, you just got to wrap your head around all the possibilities that having two pllaceable portals gives you.
Koei Warriors Series (the Dynasty, Samurai, and Orochi gammes)
Mostly the Dynasty Warriors, I love the story and characters from that series and I have loved it ever since the Romance of the Three Kingdoms games back on the early generation consoles and, even before that, Destiny of an Emperor on the NES. Dynasty Warriors got me to play Orochi, and Orochi got me to play Samurai Warriors. But Dynasty will always be my passion.
Aliens vs Predator
Been an AvP fan since the first shooter came out on PC back in the 90's. To this day, I still say that AvP2 on the PC is one of the best shooters I've played. And this generation's incarnation of AvP did not disappoint me by any means...frickin' love that stuff.
Annnnd I'll round things off with my favorite Ninja simulator: Tenchu Z.
While it doesn't have the greatest looks of this generation, I just LOVE working my way around a level, picking of the guards one by one. It's almost a puzzle game in that you have to determine which guards to take out in which order so as to avoid being spotted by another guard on patrol. And every now and then you pull off something that's truly ninja-esque and it makes you feel even better.