I don't think it's as strong as the original [REC], but that's only because the first film could start from the beginning and gradually creep up from nowhere on you. They're both outstandingly good horror movies. This one is adding something new rather than just rehashing its predecessor and it'll makes you want to watch them both back-to-back in the light of what you've just learned in the sequel. The existence of each film improves the other and I'm very happy to learn that Filmax are planning to continue the series with [REC] Genesis and [REC] Apocalypse. The former's obviously going to be a sequel, while the latter is... well, I'll give you three guesses.
The "2" in the title is a superscript (i.e. "squared"), by the way.
The obvious comparison you'll hear is that this is Aliens to the original [REC]'s Alien. We start with a bunch of soldiers with head-cameras, getting ready to enter the mansion block where everything's gone bad. They also have a civilian tagging along who knows all the answers and is quick to issue orders, but isn't exactly forthcoming about sharing his wisdom. "What are we looking for, anyway?" says a soldier who's been told to study everything in the room and get it on his helmet camera. "You just record." Watch this film, then tell me that in a certain light that guy doesn't look so vampire-like that it's creepy. Anyway, the military have some nifty tricks with their cameras, such as switching to someone else's feed and seeing it remotely.
Soon enough the body count begins and our grunts become less tolerant of getting the brush-off from their civilian. They demand some answers, which turn out to be interesting. The movie shifts genre. Not in a big way and certainly not enough to change the basic facts of the situation, but it's enough to add further implications to what we thought we were seeing. Personally I liked it a lot. It has unexpected consequences for what had previously been a kind of story that's very familiar, albeit extremely well done. All the usual gore and death is still beating down the door to get at our heroes, but the story's options have been expanded a little. This is the kind of thing a sequel should be doing, in hindsight fitting so well with what we'd seen before that I wonder if the film's producers hadn't been planning it from the beginning.
That's Act 1. It's good. Act 2 unfortunately involves three teenagers, whom we first meet as they strap fireworks to an inflatable sex doll. There are interesting things in this section, such as the overlapping timelines with Act 1 and the very bad thing our new protagonists discover, but the walking meat sacks themselves are entirely obnoxious. You'll be happily waiting to see them torn to giblets and they practically turn the film into a black comedy. They are so rubbish! Guaranteed to screw up in any situation and then expect the world to save them because they're teenagers, they deserve everything that's coming to them and the more miserable and desperate they'd get, the harder I'd be laughing at them. "Tell them we're kids; we haven't done anything!" Ahahaha, drop dead.
If nothing else, though, this section has a memorable kill. You'll know it when you see it. I also appreciate the fact that the producers cast real teens, rather than twenty-somethings.
Act 3 brings it all back though. Stuff comes together, the scriptwriters throw up a particularly surprising story idea and there's a fairly cool ending. It's not a stone-cold classic, mind you. I felt something slightly inconclusive about it, as if it's ending on one foot. It's a "middle film in a series" finale, clearly setting up [REC] Apocalypse. However it's still pretty good and at least they're not just doing the "last survivor dies" ending you tend to get with mock-camcorder movies, e.g. all of them, really.
The actors aren't really making much impression, except for that creepy badass civilian (Jonathan Mellor?). I like the cast, but this isn't a character-based film. It's about death jumping out at you and screaming in dark confined spaces. Mellor though is great. He's got a skull-like face that's perfect for... well, anything, e.g. fierce intensity, being a cold bastard or whatever.
As I've said, I think the original was better. It scared me more, it could take its time with the build-up and it had an engaging and cute lead actress. In contrast this film's protagonists aren't particularly sympathetic, especially with me choosing to take sadistic pleasure from the suffering of the idiot teens. However this is a sequel to be proud of. It's in no way letting the side down and it's got richer ideas than the first one. I can't think of a reason for any horror fan not to watch this. It's in Spanish, yes, but this is hardly a dialogue-based genre and I shouldn't think you'd have any trouble with the story even if you turned off the subtitles. It's fast-paced, energetic and pretty much guaranteed to slay an audience.
The nearest thing I have to a criticism is that the ending isn't the conclusion that it might have been, but I'm sure it'll feel exactly right in a few years time, once we've seen [REC]s Genesis and Apocalypse. This really has been a great decade for foreign-language horror, hasn't it?