Yes, it is a casual games site, but they also carry a lot of point-and-click adventures, RPGs, and strategy games like Risk that were commercial releases that are now downloadable...
And as for casual games, they are the makers of Mystery Case Files games, which are excellent, and they have all the PopCap games like Peggle etc for $12 with the coupon.
$12 is better than spending $30 for the exact same games on DS and PSP... Half the games coming out for those platforms (especially DS) are at Big Fish in better and cheaper forms...