Tales of Hearts R is a definite must IMO. Ys Memories of Celceta was fun when I played it but I didn't finish it. Freedom Wars, Soul Sacrifice Delta, Toukiden 2 (maybe Toukiden Kiwami if you can find it for cheap) for Monster Hunter style action RPGs. Senran Kagura Estival Versus for a beat 'em up game (it's fun at the very least), there area couple of the Warriors/Musou games on Vita as well. I liked Atelier Rorona as well, still have to play the other two games of that trilogy. The Atelier Dusk games are apparently good but I haven't played those.
Conception II isn't a great game but I enjoyed it. But it's a dungeon crawler with waifus.
Maybe the Jak and Daxter trilogy, even if it's just for the first game. I haven't played the Vita version though since Ihave those games on PS2.
I'll update my post if I think of anything else.