#1 - For me, without question, Castlevania Symphony of the Night. It was the perfect blend of combat, boss battles, exploration, puzzles, rpg elements and to top it off the game was massive. This game just had it all and to this day I can replay it any time and have more fun playing it than most big budget games out today. Not to mention it probably took a fraction of the money it takes to make games today. I need more 2d in my life these days.... 
#2 - Noitu Love 2
Before I say anything. Go get the demo for this game right now at http://www.konjak.org/. It was made by 1 guy and it is amazingly fun. Awesome old school action. It also just came out recently.
Instead of writing about the game here il just link this good 1up review of it. http://www.indiegames.com/blog/2008/04/review_noitu_love_2_1up.html
The game is 20 bucks and worth every dollar if you ask me.
edit: any 2d games as long as they do not use polygons, not just platformers.
#2 - Noitu Love 2
Before I say anything. Go get the demo for this game right now at http://www.konjak.org/. It was made by 1 guy and it is amazingly fun. Awesome old school action. It also just came out recently.
Instead of writing about the game here il just link this good 1up review of it. http://www.indiegames.com/blog/2008/04/review_noitu_love_2_1up.html
The game is 20 bucks and worth every dollar if you ask me.
edit: any 2d games as long as they do not use polygons, not just platformers.