Just played the demo, and I really don't like it at all. I'll describe it in a few words: XCOM but wonky.
Yeah it's marines vs aliens... except the art style and 3d models for the characters look awful. The camera is also pulled in really close so that you can't see anything. This means that you get to stare at your character's ass for twelve years while the opposing team's turn happens. I understand that they don't want you to know the location of all the aliens, but their turn takes quite a long time, and you cannot skip it like in Fire Emblem.
Another gripe I have is with the actual shooting. Whenever you take a shot, there is some invisible aim penalty that you can't really see, and nothing seems to change it. Your range for shooting enemies is also rediculously short. If you see an alien, you'd think you'd be able to shoot it because you have a gun, but nope, you have to get in its face. At least the aliens don't wear glasses, because their vision is terrible too. For some reason, Nintendo really tried to drive home this overwatch mechanic even though it isn't new or exciting, and it works pretty badly. For some reason, your aim isn't further penalized when shooting from overwatch, and you can shoot multiple times out of overwatch. Yup. Multiple times. If an enemy tries to shoot at you after you've overwatched them, you will be able to shoot them AGAIN from overwatch. The same goes for you, the player, and an overwatched enemy. Trying to best an enemy in overwatch is a gigantic pain in the ass. some characters don't stand a damn chance against an overwatched enemy.
So basically mechanics, art style, and the fact that I don't really like steampunk have driven me from this game.
Also Marth's voice actor is really bad hahahahaha