Honestly 40 bucks is a lot for a multiplayer-only game for me too, though it is better than 60. The game is fantastic, but a little light on modes at the moment (I am aware Blizzard will add more). I got the game for free, which probably does influence my feelings toward the experience I'm having.
I also have to point out that I absolutely love the maps in this game. They're all really bright and colorful and fun to look at, not to mention laid out in a way that offers a lot of strategic opportunities to both attackers and defenders.