Paper Mario: TTYD because...Yeah, I'll spare those who already know...
Also notable mentions include Fallout 3 for giving such an amazing and radical change to the series is such a way that not only takes everything from the first games and makes them available in First or Third person, but also tacks on many other things on top of the transition that makes the game go more than a step forward. Pikmin 2 deserves to make the list since it built so much more upon the formula of the first game, which rocked so hard, just needed some adjustments. Gears of War 2 because Horde in general is amazing, however the story is...Lacking, to say the least. Among some others.