I played the demo, wasn't sure about it, bought it to see whether or not it got any better.
Overall I think it's fine. It's not brilliant and I think the huge amount of marketing it got made it look like a far deeper experience than it is, like it was going to be a huge AAA console seller exclusive which just isn't what Marvelous release, but I think if the demo interested you at all then it's a decent game. I keep going back to it at least.
It is repetitive despite the amount of mission types there are, they mostly all end up with you doing the same thing of "shoot all the dudes". Escort/protection missions have you at least defending an objective (which will be destroyed if you don't prioritise targets), there's a few big bosses that are kinda neat (but do have way too much health making them a bit tedious towards the end) and there's some missions where you're on foot outside of your mech usually to sneak in somewhere and steal an enemy mech.
The auto aim is very generous but on the other hand, I don't think the game would be playable without it. That said, the game isn't about accuracy, so it doesn't provide too much of a crutch.
Melee weapons are awful, pretty much my only definitive complaint. Their range is short, it's easy to miss and there's a lot of delay after an attack. They're alright against slower bosses.
Character/mech customisation is neat. There's a lot of options with mech's to make one suited to your playstyle, which isn't something I say a lot for games.
Multiplayer I've not touched.
Story is there. I can't comment on the quality because I've been skipping it all, that said, I'm skipping it because it seemed lame.
I'm still picking it up and playing it, it's fun enough to keep me coming back. It's a perfect game to pick up for 5-30 minutes, I don't think I could spend all day on it though.