I've found that the keyboard is a little cramped for gaming. Also, having the d-pad on the right takes some getting used to, unless you set the directional buttons to wasd. I personally have started setting left right to d and f, and up and down to j and k so I can do diagonals easier. That is really the one thing that makes the n900 spectacular for gaming is that you can map just about anything.

As for sixaxis support, that looks like it would be perfect for gaming, but it's not as portable as some would like.