Super Mario Galaxy: This game made me fall in love with Nintendo again. After a string of shitty 3rd party shovelware games, I was beginning to lose faith in Nintendo. Super Mario Galaxy is hands down the best platformer I have ever played. The level design is incredible, far surpassing both Super Mario 64 and Super Mario Sunshine and the bosses were fun/awesome. The OST was incredible, I even bought the soundtrack on Ebay. And best of all, LUIGI WAS PLAYABLE!!!
Super Smash Brothers Brawl: Despite causing me a ton of heartache competitively (almost all of my favorite characters were terrible) it was still a fun experience. I LOVED Melee, more so than any other game ever created and naturally when I found out that they were making a sequel I freaked out. Me and brother easily doubled our playing time, spending at least 1000 hours of gametime playing Brawl. The cast was diverse and awesome despite various criticisms, and the single player coop was really fun. It was an incredible experience and it would have been the best game of all time imo if it was balanced competitively.
Final Fantasy 9: The best Final Fantasy ever. The characters and stories easily surpass every other title. The battle system in FF9 was a ton of fun and I loved how each character was unique instead being slight variations of each other like in the previous FF games. (FF8 i'm looking at you) FF9 is the only that I have beaten multiple times.
Earthbound: Earthbound is unique. Unique in its gamplay, story and characterization. I can still vividly remember every aspect of this game. I specifically loved travelling from Onett to Twoson, Threed and Fourside (One, Two, Three, Four) it was like one big grand adventure. I can totally understand if people who haven't play Earthbound don't like it / think its overrated because it really doesn't seem that special until you've actually played it. The soundtrack in that game is simply amazing, it actually transformed me into a Beetles fan! I slightly prefer it to Mother 3 because I liked the open world feel compared to Mother 3's linearity. (I was sad when you couldn't PSI teleport) but Mother 3 is almost as good for the reasons people before me have listed.
Ace Attorney Investigations: Ace Attorney as a whole is amazing, they're by far the best visual novel games I have ever played, but AAI specifically was a masterpiece. Its often regarded as "inferior" to the Ace Attorney games for some insane, and I don't understand why, this game was fantastic. The 5 cases were awesome, with amazing villains and surprising plot twists(the final case was a bit too long but it was still extremely good) and I loved the characterization (They really fleshed out Edgeworths character.)
Honorable mentions: 999, Wind Waker, Pokemon Gold, Kingdom Hearts and Advance Wars: Days of Ruin