I'm now please to say that I've graduduated. I've completed all 50 phases of the medium level! Hurray for me! (Lets face it, I'm sure you're not saying that, so let me have a little self-congratulatory praise for a minute...sheesh.) Although, even though I completed all the phases, my score still doesn't rival some of the board leaders. I'm a little confused...I only let 4 creeps through, yet my score is a couple of thousand less than the leaders. How is that possible? Can anyone clue me in?
Anyway, I figured I'd share my maze with you, although - after looking at hundreds of other mazes, I've come to realize its less about how the maze looks at the end than it is about how you put your maze together in the first place. And in what order you upgrade your towers. At any rate, here's what I looked like at the end...
Basically, once I'd created the majority of my maze, I just started upgrading one of each of the towers - one at a time. All of the little Pe towers you see upgraded (the ones that aren't fully upgraded, that is) I upgraded during the last phase, just to try to deal with the onslaught of creeps. Aside from that one breach of ettiquette, I adhered to my ground rules - one tower at a time until it was completely maxed out.
My advice comes with no guarantees, but if it helps you beat my score - more power to you! If it doesn't help, well, I just don't know what to say to that.