My wife really likes this game. I started playing it, so that she had an at least semi-competent co-op partner. I had fun with the game for awhile, then I hit a wall. No matter what I did, I could not win PVP and just struggled.
My wife built me a new team and not only does this new team require some actual thought to play, it's actually solid. It made the game fun again. You don't need to spend any money to enjoy this game or do well. You may need a little luck in your draws though.

Not a bad mix of the tower defence and merge genres, I've had some hectic and fun games. Also appreciate that there's a coop mode. The pay-to-win aspect and repetitive gameplay meant that I ended up only playing it as a social activity together with my significant other though, not because the gameplay kept my interest.