I fondly remember spending 2 weeks completely disassembling Sonic the Hedgehog once, I was always curious how games worked. Disassembling them turned into a little hobby of mine -- you always find leftover graphics, dead code and sometimes even whole unused levels when you poke around, it's lots of fun.
If you're still interested in game archaeology, I would highly recommend you visit The Cutting Room Floor ( http://tcrf.net/ ), a wiki dedicated to uncovering unused/development-related content in early video games. Sometimes authors even put long, rambling messages against their coworkers into games (see the page on Erika to Satoru no Yume Bouken).
Yeah, I know the guy who runs the wiki, he's a really cool guy and has been doing this for a while too. The whole wiki is fascinating if you're into that sort of thing and have some spare time.
I am a huge Sonic the Hedgehog 2 fan and I remember being on SimonWai's site back in the day (~10 years ago?) and Sonic Retro.
Anyways, it's a small world. I definitely recognized your nickname from the Sonic forum and I think you helped unearthed a prototype(s). I can't tell you how much I appreciated your work!
If you're interested, up-to-date versions of Sonic the Hedgehog disassemblies can be found here: http://info.sonicretro.org/Disassemblies
People have also disassembled other games like Super Mario Bros., etc.