depends on your choice of games. If you plan on playing massive multiplayers online, more cores will be better (i5). If you are just planning to play rpg's on single player modes then i3 would suffice.
Games are starting to get better threading and more core utilization yet they are likely going to be able to use three cores maximum. One to handle the game engine, one for better game physics computation and third for the HD audio.
But the moment you go massive multiplayer, a quad core will be much better that the hyperthreading dual core i3. users have confirmed that dual core cpu's tend to stuggle a bit while playing BF3 in multiplayer with 60 players on a map.