Sonic & Knuckles - A solid final installment of the Classic Sonic series, whose Lock-On feature encouraged replay-ability and rewarded loyal fans with lots of free content.
Bioshock - An FPS that excels in gameplay, story, and atmosphere, that had a great risk and reward system that ultimately pays off in the end.
Uncharted 2 - A sequel that took everything that was great about its predecessor and piles on tons of extra content, featuers, and gameplay, which includes a very fun, unique, and competitive online multiplayer.
Assassin's Creed 2 - Taking the foundation of the first AC and doing away with its tedious repetitive formula by including a flexible and enjoyable combat and counter system, large expansive maps to explore, varying missions and subplot that yielded great rewards to your character and the story, and giving us one of the best protagonist in the franchise.
Kirby: Mass Attack - Another example of a re-imagined Kirby title done right, this game takes away Kirby's signature copy ability in favor of 10 versions of himself to gnaw on foes and dog pile all obstacles. Aside from being a very competent title brimming with extra content, it is also a must-own for any Nintendo DS owner, as it utilizes the touch controls brilliantly.
Tetris (almost any iteration, really) - Simple in design and execution, it's a puzzle game whose only difficulty and replay value are determined solely on the player, which makes it a very enduring and fun game to pick up and play.
