I took the ACT, so I'll compare it to that.
The MCAT you need to walk in with much more factul knowledge. Only on the verbal reasoning section is all the information you need to do well found on the test.
Format is somewhat similar to the reading comprehension and Biology ACT sections. You are given a passage, you read it and answer questions about it. the differences in this are 1. The above where not all info needed is in the passages and 2. There are a few stand alone question that have nothing to do with the passage.
The MCAT is now on a computer, so you should practice accordingly (computer practice tests, reading on a computer ect).
I actually felt that the time limit was much more forgiving on the MCAT, but this could be because I actually prepared for the MCAT.
As far as studying goes I think lots of practices tests are the way to go for both.