It was okay! I loved it and had fun with it :-)
Good gameplay loop. Charming graphics/animation. I did find myself laughing whenever I won or lost because of the taglines beneath the menu text. I loved the chaos that ensued after a while during the later waves. I couldn't stop laughing after placing down like 30 shotgunners and just watching the enemies getting fried with loud ass noises.
My only real complaints lie in the sounds being EXTREMELY loud and repetitive after you put enough guys on the field. I also found myself running out of room to place the little guys, because it just got too crowded. That and the music is just a little repetitive as well (that western stage especially got grating after a bit).
I would suggest adding the option to trash/sell your little guys to make room on the field after it gets too crowded. You could also make the maps have a little more variety in terms of paths that the monsters can take, if that's possible! All suggestions, just idle ideas I had while playing the game. What you have here is great!
Keep up the great work!