I played this for a bit as well. I only got around to using Link and Megaman, but I'll give the other characters a chance soon.

It was interesting. Even though I only played the two characters so far, you can tell that each had their differences in terms of how they are handled, so it's not just a gimmick to be able to play with other NES characters. One thing I really noticed was that Link couldn't break blocks when he hit them, even when he was powered up (thank goodness he could actually jump on command though, lol).