The main problems with the game, such as they are, would seem to be 1) there's a fair few items and whatnot locked away permanently behind premium currency, social networks or paywall structure. They are not essential (or they don't seem to be), but it's either very, very unlikely you'll get them without paying, and some you definitely won't get at all. Plus 2) most of the time you'll spend playing the game - unless you drop a ton of real money for some reason - is essentially grinding to unlock the next story mission.
It's fun grinding, mind you; it doesn't feel like something you're being forced to do, and even the "hard" grinding missions aren't too hard (or at least not yet). It is very difficult to get to a point where you've got absolutely nothing you could be doing - if you put the game down it's more than likely because you want a break. At the same time, it is still grinding. It's a very particular type of game with easily recognisable gameplay patterns you've probably seen countless times before.
But for what it is, I'll say it again - it seems startlingly well done. It's a F2P base builder with a simple combat engine and randomised missions to flesh out the story, but the art, the music and sounds are lovely, both parts of the game have some depth and need a bit of skill and thought to do well, and it's never aggressively F2P to try and bully you into paying out real money. If you like this sort of game it's an easy recommendation. Definitely one of the more unexpected surprises I've had this playing games this year. (I still won't forgive Ubisoft for Trials Frontier just yet, mind.)