Quite a poor hack here. The main concept is cool, I like to play as Mario enemies in hacks, but the rest brings the overall factor down quite a lot.
Design is very repetitive overall, not much going on trough levels and a very linear one. The castle is probably the level I liked most, mainly for the idea it went for; but again, the execution is poor, and makes it indeed a poor level.
Aesthetics-wise, it's okay I guess. The author used many GFX together with vanilla tiles in a few levels, and overall it's not that bad. I'm hurted by the fact that the status bar has silly colors in some levels. Speaking of it, I assume the rex's name is Mario... isn't it? Player-wise also, the rex is very poorly animated, it has almost no other frames other than being squished and the normal one. Pretty superficial work.
Overall, not a great hack. It's not a total waste, but don't expect it to be this good hack.
Note: this hack and this one look awfully similar. I'm guessing the author here used superwiidude's demo as base and made his own. Shame...