Newer Super Mario Bros. Wii is a great music choice for games like these. Anyway, I would like to give you some criticism regarding your levels: Make sure you stick to one style. I am a very picky former level judge and despise game-mixing, otherwise known as palette-mixing. SMB3 is a traditional style, though; I advise you to download this pack:
http://www.smbxgame.com/forums/v ... 9716#p9716. However, if you stick to any other style, choices will be very limited, but of course, it's entirely up to you if even want to stick to any style in particular. Also, there are quite a bit of scenery issues. Some things like overlapping background objects are subjectively realistic, but in my opinion, it makes things feel cluttered and excessive. Additionally, you shouldn't have a yellow fence with a blue end; sticking to the blue fence would be perfect.
On the contrary, the image with Bowser looks all right, but again, you are clustering background objects. Moreover, a talking poison mushroom is a bit cheesy, right? And lastly, I recommend you either use the SMB3-styled SMB1 Bowser or the default SMB3 Bowser because the SMB1 does NOT go well with SMB3 because one style is realistic and one style is simplistic.