At the moment I'm pretty into Ace Combat: Assault Horizon Legacy on the 3DS. Luckily when you beat the campaign on any difficulty it lets you keep your purchases when starting over. The only real gripe I have is that I've beaten Easy and Normal, I'm halfway through hard, and yet at least half of the available planes aren't unlocked.

Speaking of difficulties, I have to say both Easy and Normal are easy as shit, and so far I've only died once (halfway through hard).