When I considered buying the GCW, I was ready to forget about enjoying SNES games with it. The reason is that I'm very aware of the resolution issues. As you know, one of the strong points of the GCW Zero is displaying games in native low res. The fixed low res, however, has also disadvantages, for instance, games with high resolution or games with res modes that have different aspect ratios. Unlike the Megadrive, SNES features 256x224, so the games are displayed with big vertical margins, when on a 320x240 resolution on a 4:3 screen. This would also mean that the display is compressed with a wrong aspect ratio, which would be unacceptable.
However, I've been testing the emulators on PC after investigating about the issue of the SNES's games aspect ratio. I don't know about the actual console on a CRT TV, but now I can tell that 4:3 is not the right aspect ratio for it, but 8:7. This is very easy to notice, just by looking at what is supposed to be a circle or a square on a game's graphics. Also the company logos look clearly stretched if you configure the emulator to use 4:3. Actually, it's also easy to see by taking snapshots of the same game on the Megadrive and and SNES, and comparing them in Photoshop. Maybe there were some games designed for 4:3, but I haven't found one in my selection of games yet.
Therefore, if you don't mind the smaller display, most SNES games will just look right with their almost squared screen. That's good news because this console had dozens of good arcades and it will be great to have them on my GCW Zero.