Awesome, but gets very tedious afterwhile trying to level everything up, few more types of towers, and more creeps, and different maps....then be great game. Good concept though
Wealth and Splash Slow towers in one area, with pure gems in the other area. Two areas start building the slow and welath towers first for $, then work on some pure towers, this strategy for levels post-7, worked well for me. All gold medals, on the last level now...
I use splash poison, triple dmg, and life steal and having no problems, seems to work great. But yes create towers where they can hit enemies twice, def makes it easier to send the next wave quicker. I'm sure there are plenty of workable strategies.