I've been playing it for a few hours and have cleared 4-5 stages, it's not hard but like any tactics game it really draws you in and kills time if you aren't paying attention. I'm not a fan of being forced to return to the house instead of proceeding on to the next stage. They really want you playing it over and over and over to unlock and use different units, which is a setup that works better in a roguelike. I'm still enjoying it but it gets tiresome slogging through old stages again and again before you're allowed to move on. But that said, they did make an effort to toss in a variety of events and mini bosses, giving older stages some depth.
As for mechanics I dislike how vague abilities are, there's limited information about range and some of the finer details for enemy attacks, which can be frustrating. You should be able to tell at a glance the range of your attacks and new abilities before you take them in a level up. I'm not a fan of the art style either but after awhile you stop caring, as others have said the music is good. It's a decent game all in all if you don't mind playing through the same stages repeatedly.