This demo is excellent! The difficulty is perfect, the music choice is great and the graphics fit perfectly. The levels are not too linear but not too messy. Oh, and the bosses are not crazy like we tend to see in other hacks. It is a very promising hack overall.
I'm giving it 4/5 just because there were some blind jumps (maybe a line of coins would help?) and because the last boss was a little bit too much. Apart from that, I've enjoyed it and I can see that you worked hard on it. Congrats!
Although not my cup of tea when it comes to SMW Hacks it is clear there has been a lot of effort put into this. There a few minor issues but they don't detract from the the main experience.
The first two worlds are lacking in terms of variety however the selection of different obstacles and hazards picks up in the last two worlds.
Its a pretty substantial demo in terms of how many levels it lets the player get a chance to play however I do feel some tend to drag on a bit too long.
Overall though its not a bad hack. Its just a bit bland.
Regardless Nice Work Infinity.