My amateur opinion...obviously, if it's for a collaboration, then other stuff will be added, so it's hard to give any constructive criticism that may be totally useless depending on what's added. HOWEVER...if NOTHING else is added, you could do the guitar sound a world of good by taking out some of the low mids and giving a slight, narrowish boost in the extreme top end...like 12K. Right now, the guitar has a really boxy sound that can be cleaned up a lot...Mess around by taking out stuff between 200 and 600Hz and see where it brightens up the best without losing too much body.
The vocal sound has some real problems in my opinion. The top end is pretty harsh, but still undefined at the same time...I'm not sure how much of that is the result of the verb/echo you're using, but if this were going to stay as an acoustic piece, I'd try the vocal a LOT dryer...
Oh, and if I didn't mention it, I'm a hack, lol.