The i3 should be better for gaming than the FX-4100. The Bulldozer architecture is optimized for multi-threaded performance, which the 4100 cant deliver on only being a quad core.
But saying that, they will game similarly given that they will both be using the same GPU. The GPU in gaming situations is always the bottleneck (if it isnt the game itself).
Its a Micro-ATX motherboard, so crossifre/SLI is out of the question, and you wont be able to overclock it (or use Ivy Bridge CPU's without some BIOS updates. So expandability wise isnt very good, but thats a common disadvantage to pre builts.
If your are investing this much money (~$1000 from what I can tell), you will be better off building your own machine.