Split my mind dude!
Master this shit(Y)!
I'm feeling mixed emotions here so bare with me :P.
OK, this is not a good demo I'm hearing. But the reason I also love this (I think I'm high right now XD) is because I'm hearing the basis for a GREAT song.
The beginning riffs are not something I'd want to hear on a Slayer record, Killswitch Engage, or any other metal band because it's a bit bland. I'd recommend a constant drum beat that ISN'T following the rhythm of the guitars, but diverse enough to get alot of attention. Which brings me to the guitars.
On a Metal track, I'd usually be hearing a rhythm guitar, with the lead doing something else (which is CRUCIAL for an instrumental). I hate it when both are playing the same thing, if they're leaving silent gaps in the middle (I'm referring to the first minute of this song). The melody there is great, but the rhythm (guitar) should be doing something to keep the song going during those dreadful silent moments. I know they're not long but they can be frustrating. Unless you're going for a Slipknot-esque thing.
On a more POSITIVE note, about 1:05 onward you DEFINITELY had a great thing going here. Reminds me of something I'd hear from Bullet For My Valentine. The problem with this part though is that it was hard to adjust from the HEAVY intro to the more METALCORE (google it if you don't know). 1:40 was a nice touch, and the change to the acoustic melody was a much more bearable transition. HOWEVER, I got really bored at hearing the same thing for 30-40 seconds. I'm aware there was a lead part playing but I wish it was longer.
We're back to the heavy stuff now and again, you might want to improve the transition there aswell.
The BEST part of the entire piece was 3:27 and you had an amazing little thing going on there mate! But again, the lead and rhythm are playing the same melody, leaving those irritable silent gaps in the middle >:(. Thankfully there were slightly less noticable so thank you for that!
Er...I think that just about covers it! I would suggest making another versions of this before you try vocals.
Please don't be disheartened by that 6, that's a nice 6! He wants to be your friend!....OK I'm high. Hope you didn't mind this pretty long review and I anticipate your future works!
-Noko