Well..
First, the game is OK, at best. It does have plenty of issues. Where to begin? How about a list, I like lists.
1. Neither of your sound controls seem to function, at all (oddly enough this is a by mode/difficulty issue which kind of says there may be greater issues with the game). As another person had commented the music doesn't fit. In-fact it does get annoying pretty fast.
2. Targeting. The tower targeting AI sucks. It will target an enemy, fail to fire on it, and then retarget another enemy.
3. The upgrades, speed for instance has little to no noticeable effect. Two towers (of the same type) with different speeds next to each other seem to fire at the same rate. Whereas two towers of different types with the same speed next to each other seem to fire at quite different rates. At the same time the damage upgrades seem useless and can't even make your initial starting money competetive.
4. Damage, the HP and speed of the enemy upgrades faster than the abilities of your towers can. Even building constantly because of the delayed firing, rate issues, and HP issues it seems inevitable that enemies will get past the lines.
5. On those lines the value you get from the enemies also feels disproportionately low to their enhancements. Or the cost of the towers is disproportionately high to their value.
6. On maze mode you should add inexpensive blocks to allow us to create a maze out of something less expensive. As with path mode the initial money is not enough to stop the first wave. And luck alone will stop the enemy from getting through (I have noticed they seem to start spawning at your required gap point rather than randomly).
7. Color changes. Along with all of the other cost issues color changes become an annoying expense that considering current armaments can't hold their own against the enemy it is unlikely that a reduced force due to the cost of color changes will survive.
Overall the game is fairly well made but very poorly ballanced. I played it several times with several strategies and in several modes, and though some worked better than others. All were poorly ballanced, all could use work. I did not have the bug of enemies not following the path. But the rest of the issues did leave a bad impression. I can give this 2/5 and 5/10. Keep trying I'm sure you will get it, and I do like the idea.