Well the mechanics of combat are quite different. But the game plays pretty much the same as previous editions of D&D. I can understand people liking one set of mechanics over another, and in particular the build system is very different and hard to break, but the actual game where you face each other across the table, is the same stuff.
We're on our 4th (and 5th) 4e campaign after countless previous ones with all editions back to AD&D. I must say, combat is more fun now - going through rounds faster is much less boring. But like I said, very little else has changed.
I've never played Shadowrun, so I can't comment.