I most certainly agree with everything you said. I too found the gameplay slow and monotonous, and in an attempt to make it 'better' I tried to balance out the parameters but it ended up making most of the game too hard or easy. I also agree with the visual comments, they all looked pretty bad, especially what were supposed to be monkeys and roman warriors (which I would guess nobody knew).
Viewing post in Attack Through Time jam comments
Well, to be honest: no, I didn't recognize monkeys or romans - I thought the first wave of enemies were turtles :D
But don't lose hope, creating nice art is really hard, especially if you only have 3 hours. I suck at art and it's taking me forever. One thing you can do is to use free assets for rapid prototyping, or team up with an actual game artist. I participated with an artist in the last Ludum Dare, it's amazing how fast they get things done.