If you liked N.O.V.A multiplayer, definitely get modern combat 2. It's got ten players instead of 4, with an actual rank/reward system. I also want to second The Quest and Battle for Wesnoth especially, though there are a lot of good games in this thread.
Here are the Five I've been obsessed with lately. Solomon's Keep - mini diablo dungeon crawler clone, random ability upgrades make it challenging, hardcore difficulty is hardcore. Solomon's Boneyard - Endless mode upgrade of Keep, more spells, items, characters and unlockables, also very challenging, progressive play - you keep gold you accumulate on each play to use for purchases on the next play. Puzzle Agent - Interesting story, great voiceovers, some puzzles are a bit easy while others are complete braintwisters (especially if you play the game without using hints, which could lengthen its longevity) Osmos - Another puzzler game, however the style of play is more organic, in both gameplay and graphics. Bit.trip.beat - If you're looking for a challenge look no more, the levels are completely relentless, you will not be coddled.
I'm surprised no one added these two yet. You say you're a huge smup fan? Try out the two Cave titles: Espgaluda II Dodonpatchi Resurrection The two Rocketcat Games titles are simply amazing: Hook Champ Super Quickhook I second (third, fourth'd?) the recommendation for Phoenix Wright. I played through it once a few years back and replayed it on my iPod Touch after it was released and it's still great. I got two playthroughs out of it (forgot a lot of what happened the first time too, so it was ALMOST like a new game). There's Banzai Rabbit if you want hardcore Frogger like action. It's currently free too so you should hop on that (no pun intended). Xenome isn't a bad game. Haven't had many crashes at all on my 3rd gen. Jet Car Stunts. Great graphics, controls, and it's more of a platformer than a racing title. It's really great.
Rubbing salt in the wound. I DLed Espgaluda II back when it was what, 4.99? (It did the price drop thing). Woe unto me, I didn't realize I had DLed it onto the WRONG device! Ipod 2g. Welcome to Failville, population: Me. Anyohw, I love the style (HUUUUGE Radiant Silvergun / Ikaruga / R-Type / Gradius player. I even have Einhander and Gunstar heroes)...but I'm still pissed about wasting money idiotically for a game on the wrong idevice. I have seperate itunes accounts for my different devices (don't ask), so I dunno. Maybe I'll just get desperate and bite the bullet (hell).
Can't you just log into your 2nd gen account on your 3rd gen account and Dl it from there? I might be wrong though. ALSO, if you want me to remove the sentence up there^, I can if you want. ( Talking to mods) Meteor Blitz (If you like dual stick shooters) rRootage?? Battle of Wesnoth (If you like strategic TB) Red Conquest (If you like RTS)