I Think I know what level you are talking about Adam on Sonic for the GBA, took me a long time to pass it, but I did I need to get a nintendo ds so I can get Sonic Rush (since i am a Sonic collector)
Some of the levels in Advance Wars are way too easy. I haven't played Black Hole Rising, but I read that they introduced a pipeline system, where enemies can go in and emerge at the end of it, and you have to destroy the pipe. Simple yet effective.
I'll have to disagree with the Zelda 2 comment; that game is such a wonderful piece of old-school evilness... it's just so fun! Poor, unloved Zelda 2...
And how come nobody's mentioned Within a Deep Forest yet for Click games?
Thankyou for posting the link to those Sonic level maps!!! I remember seeing them a long time ago but the site disappeared. . . and there they are. They're probably one of the best ways to learn to make levels.