Huh, I haven't had that much trouble with shielded units. I put up some of those lightning towers, and it seems to deal with the shields just fine. Maybe they patched it or something.
Anyway, this game reminds me of the various TD wars in WC3, which were always my favorite TDs. If you're familiar with those, that should give you an idea of what to expect. Basically, you have to balance your defense with your offense. Better offense yields battle points, which allow you to do upgrades. After 5 or 6 games online, I've already gotten to where I'm competitive in each match. I'm not sure how the matchups work, since I'll have one match with a pro and the next with a noob. Hopefully as the community grows, it will normalize to where you're matched up against people of your own skill.
Anyway, if you like TD games, and are looking for something different, you might just like this. --- The fact that my story isn't plausible just proves that it's true.