I have played for about two and a half hours so far and I felt that the progression is very slow if you lose. The game doesn't have many modes yet, only 1v1 and 2v2, and there is a disparity between the teams that can take away the fun at times.
The game gradually introduces certain elements as you level up, but it takes a while, and the card packs are time-consuming to obtain with not a wide variety of cards and packs.
I believe the game has a lot of room for improvement, but I can clearly see it becoming more enjoyable. The card packs have a great potential for being rewarding, similar to the old Plants vs. Zombies shooting games.
Considering the launch promotion on Steam, it's good, but paying the full price, I think it would be better to wait.