Spoony gives a decent, if profanity filled review here.
Obviously both it and this review will contain spoilers. Spoony gets it pretty much right on the money, so be sure to watch his review.
Let's compare the two films shall we?
Atmosphere: The original Thing began with a sense of isolation, which quickly devolved into paranoia, mystery, and a foreboding sense of doom. In the new film you don't feel any isolation at all until maybe halfway through the film. But once the monster escapes, the paranoia has a brief moment before it turns to relying on jump scares, and then devolving into an action film cliche of a badass woman with a flamethrower gunning down aliens in the third act. It's not an exact comparison, but think Alien vs Aliens. One is a horror film, one is a monster/action film. This Thing is not truly a horror film, and Mary Elizabeth Winstead definitely doesn't have the presence of Sigourney Weaver.
The cast: The original film took some critical flack for lack of character development, but personally I think that was undeserved. All of the original actors were veteran character actors, and you could see the personality of their characters in the way they reacted to the situation they were in. In the new film you don't really get a glimpse of the personality of any but three characters, and it's a very shallow glimpse. If you asked me what either of the three were I'd answer by the job title they held in the film, because that's as far as it gets. Hell you don't even know the name of half the Norwegian victims. Whereas in the first film you felt something for the characters, in the new one they quickly get separated into three faceless groups: heavily bearded Norwegian victims, beardless American victims, and lightly bearded pompous Norwegian pricks who deserve what they have happen to them. By the end of the film you aren't even sure what happens to some of them because the monster rampages after the leads and you don't learn of their fates.
The Monster: Hoo boy. In the first film the monster was sneaky, and didn't want to be found. You don't see the monster much, it takes a different form each time, and it's smart. Obviously it learned from this film. Because in this one it takes time to transform, it's loud, and it's a rampaging Hulk. Once it's on screen, it's constantly on screen. And there's less imagination used because it tends to repeat itself when appearing. There's always a giant mouth erupting from someone's body, or placed somewhere on the critter form. Basically, it's dumber, it's slower, it's louder. You can't develop paranoia and suspense when there's a giant freak roaring it's head off crushing things and running about. You always know where it is.
The Setting: In the original there was a storm on the way, and it was apparent going outside was deadly. You don't get that feeling here. People go outside all the time with no repercussion. Also the alien ship is visited. In detail. Because the alien tries to use it to escape (isn't it supposed to be a wreck?). In the original it was established the ship was in a crater because the Norwegians were excavating it with thermite, but in this one it's apparent it's in a crater because the alien fires the ship up melting the ice above it. Also with it being the size of Times Square you'd think someone would have noticed. The American camp for example.
The Effects: There are a few practical effects in this film, and they aren't bad. Don't get used to seeing them. Once the alien is revealed we go cgi, and the cgi varies from being pretty good in the quick cut scenes to absolutely piss poor when it needs to stand out. Once you get to the ship, the Thing basically becomes a cartoon. Granted it's an icky, Lovecraftian inspired cartoon, but it's not scary.
Overall: This was originally intended to be a remake before they made it a prequel, and it shows. It shows really bad. You have newer versions of several scenes from the classic (the autopsy, the failed blood tests, etc), and you have nods to the first film in that they show how some of the Norwegians die but not others (implying deleted scenes). Instead of building characterization and paranoia, the first half is exposition. Some of which is pointless. If you've seen the first movie, you know whats happening. If you haven't, the film has no subtlety, so you don't need it explained. It kind of exists to 'explain' the first one, and only succeeds in demythologizing it. It also mentions a Russian base 50 miles from the Norwegian one, setting up a sequel as you never find out the fate of the female lead (although by all rights she should freeze to death in the snow). Then they tie it to the first film with a scene shown after the credits.
My Impression: This was kind of rushed. The cgi doesn't seem finished in some scenes, you never find out what happens to several Norwegians (implying scenes were cut for time or to keep an R), and there are huge gaping plot holes. It's a mediocre alien monster film. Accent on mediocre. If they'd tightened up the script, and took their time with the effects, and established some characters it could have been great, or at least a worthy sequel to the original. This just feels like they got lazy or ran out of money. So all in all the monster of the film is like a metaphor for the movie itself. It makes an imperfect copy of it's target that doesn't stand up to serious scrutiny. Much of what made the original special is gone, and you are left with only an imperfect copy without the soul of it's predecessor.
Also on a side note, after the boring expositiony bit when the monster is on the loose, this movie is LOUD. At least it was in the theater I saw it in. Avoid sitting near speakers or you will leave deaf.