Mass Effect 2 might be an interesting idea, streamlined RPG with shooter elements (granted they are 3rd person). But I personally believe that you shouldn't try to restrict just to multiplayer games though. You both can share and play together (you in charge of RPG elements, him shooting). Or play the same game but watch how your decisions change...Playing a great game with someone is just as good as multiplayer, sometimes better (in my experience).
You could also try the Bioshock series as well, again just play the game but make different decisions or have different playing styles. Hope this helps.