As a big fan of Tower Defense, this is my absolute favorite. It has the most natural learning curve, and the end levels are probably some of the hardest in the genre. The game truly shines in coop, however even in single player you often take just one more go to perfect the level. Scoreboards also make you want to go beyond just finishing the level flawlessly, and instead you try to make it through the level using only the necessary resources (as you are scored based on resources left).

In summation, this game is all about speed, planning ahead, and spending resources wisely. And it's oh so fun!

Don't let my played time fool you. I've played this game mostly on PS3 and PS Vita, where I can estimate around 100 hours played. Also, don't listen to most of the negative reviews here. It seems they have only played the first couple of levels, which are basically training levels.