Squished. I've never been too fond of how the majority of the the Classic NES series games look on the GBA. The only real acceptable game to me is Zelda 1, the rest are always weirdly compressed. PocketNES does a much better job with this.
The SNES controller is rounded at the ends, whereas on the GB Commander there's a lip to rest your thumb on. It might seem small, but it really does make a difference. It won't appeal to everyone, but I find that since I bought one I couldn't imagine using my Super GameBoy without that controller.