This is old (2005) but: http://www.pouet.net/prod.php?which=16402 Click download, unzip and watch with KiGB, most other emulators play it a buggy or not at all . (Also KiGB lets all of the special effects in the video play properly.)
If you're amazed at that then you never saw the Commodore 64 doing 3D in real time, and that machine is slower than the GBC :P Also 0:42 if you click the YouTube link. Actually it's pure raster effects >_> but it still looks cool :3
Another machine that's good for demos is the Amiga. I would estimate that the Amiga demo scene is about as big as the C64 demo scene (although many demos only run on an unexpanded A500, I should know as I've had about 50 million guru meditations on my A3000 trying to run older demos).
And just when I thought Harry Potter and the Chamber of Secrets (As a whole), as well as Cannon Fodders space eating FMV sequences were among the peaks of creative use of hardware on the Game Boy Color. Heh, this thing actually runs better than the mentioned games on Lameboy (For DS), the above games would have all sorts of horrible rastering errors because the emulator simply isn't fast enough, yet not too many happen with this tech demo (The beginning certainly broke it though). Now, perhaps I am being arrogant, but 5mhz is nothing to scoff at, I mean, the Mega Drive had 7.7mhzish power on its main CPU. I'm no programmer, but those numbers gotta mean something.
The Mega Drive has a 68000 processor as its main processor though and it's able to easily address more memory and is much faster on 16-bit calculations than the GBZ80 (especially since the GBZ80 lacks a lot of the cool instructions, in fact making it nearer to the 8080 than the Z80). So its power is nowhere near that of the Mega Drive in the end.
Not as cool as mental respirator, but this is worth mentioning: http://kigb.emuunlim.com/demo3d.zip Most people probably played that when first downloading KiGB. Note, this is on a system almost half as fast as a GBC (~8MHz vs. 4.19MHz or something).
Not special. I've seen real-time raytracing, tesselation, and digital modplayers done on the c64. However, the most impressive demo I ever saw was this: http://pouet.net/prod.php?which=51983 It literally pisses in the face of every limitation the c64 has. No windowing, runs in high resolution and full 50fps almost everywhere, and the music is way the fuck more than just 3 channels.
Er, that too, although next time make sure that the download link works. Either way, my point stands: that GBC demo is nothing compared to several demos on the C64, especially certain recent ones...
Except that the GBC demo is mostly a VDP abuse while C64 demos do most of the stuff in software. And the C64 is in theory weaker than the GBC in terms of software processing power.
Except the C64 has been around far longer than the GBC so demos for the C64 are more practiced. Which is the point I believe chimpo was trying to make.
Many C64 effects are done by abusing the VIC-II on a cycle-exact level per scanline. Plus, isn't the 6502 more efficient per-cycle than the GBZ80, at a raw level?
On the subject of games that push the crap out of the Game Boy Color. This is pretty much a raw PCM rip of ALL the audio from Cannon Fodder, it seems to store everything as 4000hz 8-bit unsigned PCM samples... not that the word 'sample' applies to this game. Edit: Actually it could be 5000hz... play it at 5000hz if you can, but 4000hz also gives you a rough idea on what it sounds like.
You know, I'm really surprised that the vast majority of Game Boy emulators still don't get the sampled sounds right. ...Or the SNES-exclusive sounds in some games, or the fading in the Super Game Boy frames or, in some cases, even the special color modes in the GBC. It's like development in them is always halted when they're good enough to play the most well known games.
The vast majority of people don't care about accuracy, as long as their games run "right". Look at how long Nesticle persevered - I think it died because it stopped running acceptably without being run under a VM like Dosbox, rather than dying because people realized it was shit.