The CD32 version of Chuck Rock and Chuck Rock II unfortunately still use the OCS A500 version of the game, which plays perfectly and sounds awesome, but doesn't look as good as the Mega Drive version. This is due to the OCS chipset being limited to 8 colours for foreground and 8 colours for background parallax. The Mega Drive, like AGA, could use 16 colours per playfield (up to a maximum of four, and a total of 61 colours if three layers have transparent 0-colours). It's a real shame the CD32 version didn't use the more colourful, layered graphics from the Mega Drive version, since the hardware is easily capable, but I guess it was easier to port the A500 version over. Of course, the Amiga versions are enhanced somewhat by the extra colours of the raster bar added by the Copper chip.
If you have a look at Chuck Rock, Chuck Rock II, Wonderdog and Wolfchild, all Core platform games, you'll notice they all use the same or similar game engines, and all four games have nicer-looking, worse-sounding Mega Drive versions. The ST versions of these games were missing the parallax layer in the background, but the platform engine they had coded allowed for scrolling of a 8-colour playfield, which was quite impressive for the ST. I guess Core had a pretty good system for developing games simultaneously on the three different 68000 platforms at the same time.
I also have the Master System versions of Chuck Rock and Chuck Rock II, which are totally different from the Amiga/Mega Drive/ST versions. All the graphics had to be redrawn and resized, and the level designs simplified, but they're both still good games for the old 8bit Sega.
So, in conclusion:
CD32: Best music, best sound, best intro, best gameplay.
Mega Drive: Best graphics.
A500: Better than the ST version.
Atari ST: Shit.
I haven't played the Sega MegaCD version, but I'm assuming it has better graphics than the CD32, the same CD music, and not much else missing, although the CD32 possibly still has the best intro, as it could play higher colour/resolution video and animation than the MegaCD due to its faster CD-ROM drive and larger colour palette. I haven't got the SNES or Acorn versions of these games yet though, so I can't compare those. I've got a few SNESs and an Acorn RiscPC600 here so I might look into trying to find the games for them, Chuck Rock II is one of my favourite platformers.