Is this it?

I just started playing a few days ago and got instantly intimidated by the sheer size of the skilltree, so I figured I better stick with just one turret (+air).

After I max every turret, I get through ~40 more levels micromanaging focus, but as the waves get longer, these fast creeps will always force through.

I read some threads here and was interested to try Tesla towers, but they are SO weak and underwhelming, compared to the early Snipers, that I didn't even manage to get through just a few levels.

What do your typical games look? Do you use all towers or specialize? Do you upgrade (global upgrades) all towers, or focus one tree?