As much as I'm already bashing the movie, I found this user review on IMDB funny just in how this person obviously had a vendetta because there's so much assumption, it's hilarious.
SPOILERS
"I saw this is in a special preview the other night and I was underwhelmed. Sure, Channing as Duke, Byung-Hun Lee as Storm Shadow, Arnie Vosloo as Zartan and Luke Bracey as Cobra Commander are back (his suit finally looks the way it is supposed to) Jonathan Pryce as wimpy US president as well, but this pic took an awfully long time to be developed and find a release date. Now we get Ray Park as Snake Eyes and Dwayne "The Rock" Johnson as Roadblock (where has he been all this time?) A hold-over from last summer to add 3D effects and some extra scenes with Tatum, which they did in the beginning; unfortunately that meant some other fight scenes with Rza as Blind Master and Elodie Yung as Jinx had to be shortened to not be dragged down plot wise in the middle part of the movie, a fantastic fight (and flight) sequence in and near the mountain monastery where Storm Shadow has to be abducted to be brought up to speed about what Zartan has really been up to with Cobra. Walton Goggins turns up as Chief Warden Nigel James of an extreme underground prison facility and Bruce Willis gets a few good scenes as gun nut General Joe Colton, whose house seems to be a whole arsenal of weaponry - and wth is James Carville doing in this?? - I liked wonder woman Adrianne Palicki as Brenda - whoops, Jaye, but you can tell that the production as a whole struggled mightily to keep this movie to no more than a 100 minutes in edit. Scenes are set up elaborately only to be over in their entirety before you know it, in a plot which resembles the "Renegades" TV story line with a little James Bond from yesteryear thrown in (think "Diamonds Are Forever" and "Moonraker"). Directed by Jon M. Chu who took over from Stephen Sommers in this sequel, the movie offers little more than some extra VFX over its predecessor. I wished I had seen a little extra of Zartan and Jinx but oh well. Somehow this franchise seems to lend itself better to TV serials and animated stuff... great live action movies don't seem to be part of it. I marked my review as containing spoilers but most of this you can glean from the trailers already."
As for RottenTomatoes, I remember RoC was in the upper 70s, lower 80s before it was released. You have to understand that a lot of studios have paid people to go around the internet before a movie is released and counter negative reviews on sites like IMDB.com and Rotten Tomatoes by giving movies a lot of positive ratings. In essence, they're trying to protect their investment and maximize their opening earnings.