Tell me what you think

A casual gamer should survive more than fine on that.
It's just me but I prefer full-towers (ability to place more cooling), and personally I would replace the mobo.
If you buy the components separate (including a bump from 800mhz RAM to 1066 or 1333) you would run to roughly the same price or lower.
The 9800 GT is fine for all your needs at the current time. Unless you are obsessed with anti-aliasing then i'd upgrade to a 260/280 or a 3850 - preferably the previous.