Very Cool...
First off, I have to say this has an 8-bit feeling to it. It seems like it should be the background music for some epic 8-bit rpg. Especially for a dungeon level, or something dark like that.
As for the song itself, I like it a lot. There are a few things I think you could do to improve it though.
First, you need to vary the rhythm a bit. The drums you created really just do the same cadence over and over, which becomes a bit repetitive by the end of the song. You need to vary that a bit more, maybe add some snare or something somewhere. Or just change up what you are already using.
Second, I like the sounds and how they mesh together so well. And I really like the sound at about the 1:00 mark. Where everything but that one sound dies out. I think you could add a new melody there, or maybe expand on the idea you already have there.
Lastly, I personally think you could have more of a build up to the end. Maybe add a descant part above everything that is noticeable, but not overbearing. If you don't know what a descant is, (Cause not everybody took choir in school), it is a melody above the melody already in place. You most often hear it in choral arrangements near the end of epic songs.
But all in all, this is really good. Especially considering the fact you are using the demo and can't save anything. So I'ma give ya 5/5 and 9/10. Cause it can be improved, but I remember what it was like using that shitty demo version of FL Studio. And anyone using that deserves a break on their score! ;-)
Hope this helped, and gave you some ideas.
-Gravey-