Ghost Recon Shadow Wars is an excellent turn based strategy game and is super cheap.
But the best strategy game IMHO is FireEmblem Awakening which is strategy/rpg mix.
Tales of the Abyss (great realtime RPG)
KingdomHearts3d also is.
Mario&Luigi DreamTeam is a nice turn based RPG. Paper Mario is also turn based.
Etrian Odyssey is a dungeon crawler RPG series
Pokemon
You have to get at least 1 racing game MarioKart7!
Another interesting game I just bought (for like 13€ bought at zavvi.com 2for25pounds deal) is Virtues Last Reward (I have no clue what genre it is tho. Story driven mystery/puzzler?) A little bit like Professor Layton which itself is also a nice series.
Platformers obviously Mario 3D Land (great game when you think its over it actually starts!)
maybe Sonic Lost World 3DS (depends on the reviews!)
Kid Icarus uprising is also a nice game (rail+ free roam shooter/adventure) with really high production value but beware of the controls they will drive you insane! If you are patient you will start to love the game if not then avoid it because the controls are most likely not for you.
There is also a ton of eshop games that are actually really good.
