Wafu, currently in open beta, has come out and told us exactly why we should subscribe to the game. When it launches on February 29th, it will have to levels of membership: free and premium. From the looks of it, you'll want to shell out the $6.00 a month if you want the real experience. Oh, and if you subscribe before February 27th, you can get some pioneer clothes. So yeah, there's that.
Premium membership imposes no restrictions on the player, so you're free to be and go where you want. On the flip side, the free version seems somewhat lackluster -- some of the key features like the ecosystem and government mechanics are locked out.
I've played the beta for an admittedly small amount of time, but so far I'm quite enjoying myself. I'm a huge SRPG fan and Wakfu has done a great job of blending the fighting mechanic into the open MMO world. It doesn't feel forced and battles flow pretty naturally. I'm also looking forward to getting more involved in the politics of the game to see if they actually work like I want them to.