ZZT

The Good
Though its simple, ASCII graphics were dated even when ZZT was released, it was such a robust tool for game creation, that it's still popular to this very day. While there were certainly limitations to what you could do with it, ZZT was a perfect starting off point for any would-be game developer. There were plenty of pre-packaged enemies and tools, but with ZZT OOP (ZZT Object Oriented Programming), a creative user could make anything from a custom baddie to a fairly complex RPG battle system.

The Bad
As I've said, ZZT doesn't look very good. It doesn't sound very good either. While that doesn't take away from it's overall appeal, it will most certainly provide a barrier to entry for folks accustomed to the prettier things in life.

The Bottom Line
ZZT was one of the first truely community driven games -- I remember downloading games from AOL's media library back when AOL WAS the internet. It's a fun game in and of itself, and there's a huge library of free, community-made games that add to an already impressive package.