In your opinion, what is the best looking cartridge format? For me, I think it's probably the Super Famicom cartridge. It's so perfectly rounded and smooth, and I like the little ridges on the back. I'm also fond of the warning label that goes on the back, which is in all Japanese. It's certainly a lot cooler looking than the American SNES carts, which have a similar design to the ugly American SNES. Another one I like a lot is the Japanese Mega Drive cart. Very futuristic and cool, and again it has a cool warning label on the back. Not sure why I like those so much. I also love N64 carts.
Cartridges are cool for many reasons, such as short loading times, durability (they can't be scratched like CDs), and the potential for additional hardware (i.e. Super FX or Sega SVP). Mainly I just like the idea of plonking a big plastic digital hunk of stuff into my videogame console. They're like tapes, in a way, except that they don't move - as someone said in an earlier thread, they sometimes called cartridges "cassettes" in Japan.