Well I do like where your voice sits, however I feel as though it is a bit too monotonic and just needs a bit of flare every now and again to maintain a fresh sound in the air.
As for flow, it just seems a bit too slow for me personally, sort of monotonous. Also, the rhythm seems to be just eighth notes through the whole thing; don't be afraid to add some variation to it! Lastly your phrases seem a bit short to me as well.
Finally about the writing and your lyrics, for the most part your lines were "word word word rhyming-word/ word word word rhyming-word/ etc." I did see a few times where you tried to come out of that scheme but it just sucked you right back in; basically change the scheme up to maintain a fresher sound. If you want to add more spice into your lyrics I'd recommend using alliteration, puns, and more multisyllabic rhyme (be careful not to overuse it). Most literary elements can aid to a great rap song.
In general just add some variation once in a while to keep the song from becoming boring. It may sound like a lot but that to me is half the fun of creating new music!
Links:
Literary Schemes and Tropes
http://bellevuecollege.edu/artshum/materials/spch/Buxton/Schemes_Tropes.htmHail Mary - Tupac Shakur (Listen to the way he uses rhythm)
http://www.youtube.com/watch?v=nkJA6SYwa94Troublesome 96 - Tupac Shakur (Make note of his rhyme scheme and use of alliteration. Also the vocal flare I mentioned is present in both this song and Hail Mary)
http://www.youtube.com/watch?v=RdX79pwyBII