Somebody know a decent tower defense game?

I´m looking for something 2D, graphics need not to be AAA, but no 8bit retro crap, plx :)
Different maps that require different strategies would be kinda awesome, also like different "races" with different towers.
MP is a must, also is building mazes.
In short, as close to the TDs in warcraft 3 as it gets, without being warcraft 3:)
o, and available on steam if it´s not too much to ask for.
Know anything?

Thanks a lot and kind regards. :)