Since I'm essentially retiring here, I'll lay out my strat.
Final Map Layout
1. Put up the Dart Tower and the Pellets closest to the spawns first.
2. Flood Wave 1-3 in.
3. No, really. The first three.
4. As they're dying, build up the bottom half of the center row from left to right.
5. Once you've dropped two towers, launch Wave 4.
6. Continue building the bottom half of the center row at Ridiculous Speed. You need to do this fast enough to redirect the vertical creeps to the left.
7. Once the bottom half of the center row is built, throw a few towers at the bottom exit to catch the vertical creeps that snuck through. Wave 5 should already be steamrolling across the screen.
8. Finish up the small "blocker" at the bottom, launch Wave 6, and complete the middle row as they drop. Make sure that the vertical creep have to go all the way to the left at the top before moving down.
9. Launch Wave 7. As soon as they reach the first tower, launch wave 8.
10. Once the first boss drops (+40), upgrade the Dart tower one level and start building up the maze from left to right. You should be able to launch up to Wave 11 one after the other as you do this.
11. Mass up 85 gold as you're able (the second boss should drop and help this out a lot) then drop a Swarm tower, launch Waves 12-16, and upgrade the tower. Get ready to throw a Pellet tower at the end of your center tunnel.
12. Upgrade the Swarm tower once the cash shows up, and the Dart tower after that.
13. Begin firing waves in clusters of four - stop at the Immunes to give yourself enough time to get the cash into your Swarm tower.
The rest is a fine balance of upgrading the Dart Tower to kill the ground-based Creep faster, and upgrading the Swarm Tower fast enough to keep the fliers dying. A second Dart and Swarm should get put up quickly so that you can account for the time required to get both of them with a final upgrade to Storm, and you
must get at least two Blizzard Towers in the middle area to knock down the L42 bosses.
My best results have come from upping the Dart Towers quickly in order to wipe out the ground-based units ... and then selling them at L41 to finance the double-Storm upgrade. Once the L42 bosses die, flood in the rest of the waves, knock down the L48 flyers, sell off the Storm Towers, and throw up the ground defense.
- M4H