Quite good for Flash Mario but wall jumps are bad!
In the group of FLASH Mario games I've encountered, this is actually relatively good. You just didn't copy the sprites from the originals, but recreated the characters with quite nice graphics, and you've taken some personal directions (eg. with the swimming) that don't destroy the basic concept of Mario. And the controls are mostly okay, except for those wall jumps, which - believe me and the other reviewers - is indeed a problem here.
As a reply to a comment regarding the wall jumps problem you asked:
"Though I wonder if if those commenting on wall jumping ever played New Mario Bros and share a similar opinion there?"
Well now I'm a bit confused. This puts me to question are we really talking about the same games? I have played and enjoyed New Super Mario Bros and definitely share that opinion! In New SMB the wall jumps are close to being the easiest wall jumps in a game ever! In New SMB you don't need to time the wall jumps as you automatically slide against the wall and can jump of the wall whenever you want. And when you jump you always have a proper jump. So I'd say the wall jumps work perfectly there. Then there are many games where wall jumps are more difficult than in New SMB since you have to have the right timing, but even in those games, once you time the jump correctly, you'll usually do just fine.
In this game the biggest problem with wall jumping doesn't seem to be timing: you can quite easily do one wall jump to reach a slightly higher sledge (like in the short introductory scene). But the problem is that usually the wall jump is just a very small nudge upwards (and I think that's the thing people are having problems with). Once you study the controls a bit you can find a way to leap away from the wall, but still the jumps reach very low, and going short distances is already a trouble. And by the way, I found the same, if not even more troublesome issue problem with that swim-wall kick.
The bottom line is that the basic controls (which the wall jumps are a part of) should be easy and intuitive. In this case the wall jumps are neither. The difficulty should be reached through challenging enemies and situations, not having to cope with difficult controls. Difficult controls just make people frustrated and annoyed.
If you can fix the wall jumps (and maybe redesign the levels accordingly a bit) this could be quite a good flash game. Still, the fact remains that the quality would still be far from the real Nintendo Mario games. Thus, like you said in the game description, maybe it's better to work on a new personal idea next. Then you can have the best existing implementation of that idea! :)