Depends on the game. If you take HD games with fairly basic gameplay that don't use too much advanced physics and AI, it shouldn't be a problem at all. We have Super Street Fighter 4 and a remake of Resident Evil Mercenaries (remake of the multiplayer mode in RE4 and 5) for reference there.
Most PS3 and 360 games don't really use the full potential of their respective consoles. Sure the visuals might look nice and all, but gameplay wise there's not really anything that couldn't have been done on last gen consoles. It's when you get to some of the more advanced games where you'll hit roadblocks. Games that use advanced physics and AI such as Star Wars Force Unleashed and Grand Theft Auto 4. They take advantage of technology that uses the raw CPU power of the cell processor and Xbox's multicore Xenon. The 3DS' CPU is likely ARM based and more akin to the power of last gen consoles. It might be able to pull off a few advanced physics and AI tricks, but not all of them at once like some current gen console games do.
If you have a current gen game that doesn't use intense AI and physics calculations, the 3DS should probably be able to do the game justice in terms of gameplay. Heck, i'm sure 3DS could handle some of the games i mentioned above, but they would have to cut out some of those enhancements (not that they're THAT important anyways). There's little stopping developers from porting most current gen games to the 3DS. Some adjustments might have to be made, but i don't see why not.