i played this for about 15 minutes and here's what i found.
#1-spray can. i never got this thing to shoot. not once. i placed it multiple places, positions and nothing.
#2-no upgrades for towers. once you bought a tower, that was it. there is no option to make it stronger or shoot faster.
#3-available money per round. you start with 200 points to spend on towers for each round. that is good for the easier rounds, but on round 3, i again tried with different towers, positions, combo's, and couldn't get a perfect no matter how hard i tried. the best i could do was with the fire tower(red) and end up with 1 heart at the end. not enough money to start with.
#4-try some different maps, instead of the same map, but different enemies.
#5-it may help to play some Tower Defense games before making one. this will usually give you some good pointers and starting areas to bring into your game. however, make it original in some way, don't just copy.
for your first TD game, you did alright. i love TD games and play them often. my Favorites so far being Bloons TD 4 and Cursed Treasure 1 & 2. You have a good start here, keep it up. i would like to fall in love with another TD game in the near future. maybe it'll be yours. :)
2/5, 2.5 stars