Ok, I appriciate its a draft version, but obvious stuff: 1) Sound, lack of. Needs fairly good effects to make up for basicness of graphics, possibly a slightly different bang depending on type of gun/explosion etc.
2) Instructions/tutorial for those who have never played TD before. 3) Nice title graphic on Normal/Hard selection. Also, to what does 'Upgrades on right cost 500' refer to? The actual upgrade button costs whatever the tower requirement is. You might be better putting the cost next to the buttons themselves 4) Mechanics are good for the most part, but in later waves speeding up locks up the whole game for 5 mins while it sorts itself out. 5) Balance needs adjusting, theres no real need to ever get new tower types, or even upgrade the ones you have, all i did was buy rows of starter towers, getting a new one virtually every wave and most baddies did not make it past the first corner. 6) A bit more zing in terms of, maybe announce Bosses coming, or countdowns to special units arriving or something?
Other than those point, operates smoother than mant TD games, I look forward to the finished version.