Codename STEAM, for sure. 3DS has become my most played console lately, and Codename STEAM is only going to add to that.
Also Forza Horizon 2: Fast and the Furious stand alone expansion. It's free, don't need FH2 (don't have it) and FnF is one of my favorite blockbuster franchises.
If I had a PS4, I'd get Bloodborne.