I admit that I did not play the original Metroid games at all. In fact, I think this is the only fan made version of the games that I have played. With all that being said, this was freaking awesome. I think my favorite part is probably how great the graphics are. It looks just like what you would see in a professional video game. The sounds were awesome as well.
It's easy to see how this has stood the test of time. I thought I wasn't able to kill the little floating guys who went back and forth. I think they can only be killed with a big blue blast. I was amazed at how long I lasted in this. Of course, this level just seems to go on forever.