I saw the trailer for this a few weeks back, I agree, I think it looks interesting. However, my nerd side means when I'm at the movie theater on November 4th, it will be to see Dr. Strange, but I'd like to watch this soon. As crazy as Mel can be, he's generally proven to be adept behind the camera, and I like Andrew Garfield as an actor, so I think this one has quite a bit of potential.
As for the Rotten Tomatoes question, the website basically compiles critic's reviews, and then has a percentage of how many critics gave it a positive review. So if a movie has a score of 94, that means 94% of critics gave it a positive review. If a movie has a score over 60, that is considered "fresh" while movies under 60 are "rotten." They also have user reviews on the same thing, so it's often interesting to me to see the difference between the two. Sometimes a movie is 20 points higher with users than critics, sometimes the opposite is true. You do have to temper scores sometimes, for a comedy, anything above about a 70 is usually pretty solid, for an action movie, you want at least a high 70, anything in the 90's is usually a good bet to at least be in the Oscar discussion.