Alright, so the game;
It's been wholly enjoyable so far. Definitely more action oriented than It Takes Two, with some combat and boss fights, but they're not what I'd call high stakes.
There's no health or lives counter, so as long as both of you don't die at the same time, they'll just keep respawning. To that end I would say if you're chill about it and don't get all angry should you be getting stuck in a section, it shouldn't feel too difficult.
There were a number of co-op puzzles that you need the other player to progress through, your usual "one person does X to the other person can reach Y" kind of thing. In general it's pretty clear what to do next though. Combat isn't too tough, it seemed mostly dodging big attacks or shit on the floor and waiting for your opening. It was the case one or two times that one of the players gets stuck driving while the other shoots, etc. and you've not got the choice as to who does it (short of trading controllers), but honestly that makes it feel more rounded. There was a similar scenario later that was reversed, so it gives both players the opportunity to do the things. Still boils down to not really feeling high-stakes and as long as you're not getting frustrated should the other player mess up, it'll be fine.
The story is pretty interesting and unique. I didn't really know the plot going in, but I dig it. At the start you essentially choose which player is going to be the "sci-fi" one and which is going to be the "fantasy" one, but you're constantly switching back and forth between them. We didn't get to any part where we were playing separately with different objectives, but I think the character choice is more just flavor. I'm trying not to give away the plot any, but there have been a couple of really fun points, especially the second side-story that you'll encounter, that was awesome.
So, I have no qualms about having purchased it. We'll definitely play through the whole thing, maybe twice so we can switch the parts we play. My one gripe might be around the saves, as it seems to just checkpoint you at certain bits and when we quit playing that'd been a little way back, but I doubt we lost too much progress.
Not sure how the experience would be by yourself without actually playing it co-op, but it's worth the purchase in my opinion.