Overall, I'm very happy with it. I think that for most people who see SOMA as an unquestionably superior title to the original Amnesia, Rebirth isn't going to dethrone it for you, but it will give you a lot of reasons to consider it an equal. This is an incredibly balanced game across the pillars of design Frictional has taken to over the years; it is *exactly* what you'd expect if you tried to consider SOMA and the original Amnesia as functions and composed them -- hilariously, the result, in a few ways, speaks a little to what A Machine for Pigs tried (and failed, miserably) to do. Take that as you will, but the DNA here is still strongly Frictional, and the end result, while not perfection by any stretch, is refined.
As people have said, Rebirth is a slower burn; it takes a little bit of time to rev the engine here, and mileage may very as the game appears to beat around the bush. In fact, there are meaningful things happening, but it takes some time to see value in it. Sometimes Rebirth says the loud stuff quietly, and the quiet stuff loudly, and it can feel at odds with itself when it does this. Monster sequences, for instance, are surprisingly restrained here, and usually are there to decorate and move the player moreso than feel like an event unto themselves -- maybe that's a problem coming from the older school Amnesia approach, but it lets the world and environments of the game breathe, and there's a lot going on in those moments. The story unfolds in a more visual way, and there are new gameplay mechanisms that push it forward still. Some beats, unfortunately, are easier to miss than they should be, but for the most part players are likely to grok the major thrusts of it.
I don't think Rebirth quite manages to make good on the promise of delivering a 'shocking' moment ala SOMA -- it's really a lot of smaller moments that add up to a surprisingly complex narrative with a lot of world building, and done in a way that is fair to the observant player: you'll deduce a lot of what is going on at, or around the time the game feeds it to you in more conclusive ways. It ends up feeling like the best kind of adventure story where you're mind keeps mulling over possibilities of where things can go, and then you actually go there. There's a lot of forward momentum and variety here, and inertia to boot once the story has heated up. This isn't to say there aren't any "what the fuck" moments -- there's plenty, and they're all a lot of fun.
Rebirth is a scary game, but the pull between ideas presented in SOMA and Amnesia means it falls closer to the former, ultimately. There's puzzle solving (and the puzzles are actually decent) and monster encounters, but they do take a backseat to keeping things moving forward in the story. Seeing some refer to the game as 'walking sim' is a bit eyebrow-raising when you consider the title holistically. Everything I expected to see here was definitely here.
The addition of the baby as a gameplay mechanic is a bit strange. It's cohesive, it works as advertised for being both a gameplay and storyline device, but it is a tad unfortunate that it kind of always feels like more of a device than anything else. Having the emotional core of the story end up in the backseat of my mind wasn't entirely unexpected, and I definitely need to consider it a con, ultimately. It culminates in an ending that just doesn't quite pull together, even though it's on firm narrative groundwork. If the story underlying everything didn't work so well, it'd be a critical issue for me.
What does work, and amazingly well, is Frictional's work to keep the game scary even when you're messing up: see, I never saw a game over screen. And I *think* that may be because there isn't one. Even though this a spoiler-ish breakdown, I don't want to talk about this too much in case the reader intends to play: the long story short is that dying in the game is treated almost as a plot point, and it reduces potentially frustration to almost non-existent levels. I can't say it's *impossible* to die, because I don't know for sure, but it sure seemed that way.