The Metal Slug games don't look as bad. I tested out KOF '98, KOF '99, The Last Blade and Real Bout Fatal Fury 2 and the graphics are very jagged looking. The anti-aliasing effect of what is normally found with scanlines is absent when running these games in 240p mode in Virtual Console.
are you sure it's actually running them in 240p mode? some later virtual console titles defaulted to 480i because Nintendo was getting reports of people having problems with 240p ( lots of TVs around the time didn't properly support the resolution and wouldn't even show a picture)
some of the 480i games (like comic zone) can be set back to 240p by using the menu trick
Playing in 240p
In order to play some VC games in 240p, your Wii needs to be set to 480i mode. Then follow this procedure:
1. Set your Wii to 480i mode (I had mine set to 4:3 as well...I'm not sure if that matters). This will not work in 480p mode.
2. Start a Virtual Console game.
2. Press the Home button to bring up the Home menu, and then click on Operations Guide.
3. Attach a Nunchuk controller to your Wii remote (if the classic controller is plugged in, you'll have to remove it to do this).
4. Press A+1+Z simultaneously (A and 1 are on your Wii remote, Z on your Nunchuk).
5. You should hear a sound confirming that you've done this correctly. This should activate 240p mode for all VC games that are 240p-compatible.
6. To switch to 480i mode for VC, follow the same steps as above, but press A+2+Z instead.