i agree with jed & KER... the m2 stuff does tend to get blasted pretty hard, and first aid does a good job of keeping it clear & concise...
that said, studying first aid to the exclusion of anything else will most likely get you a one-way ticket to your school's MedEd office for a little talk regarding why you didn't do as well as you thought, and what you need to do to prepare for the retake...
go through other sources, and write in the margins of first aid... when it becomes crunch time (approx. 10d or so before the test), you now have a concise, portable, high yield resource to concentrate on. many other posts in this thread have covered what the "good" the "bad" and the "ugly" books are for board prep - heck, even first aid has a ranking of review books in the back...
if you're interested, here was my list (in order of importance):
First Aid
BRS Path, BRS Physio
Micro Made Ridiculously Simple
Kaplan biochem, Kaplan pharm (some lippincott pharm/biochem)
High Yield: anat (just for the landmark tables, nerves, etc... most everyone overstudies anatomy) & embryo
FA behavioral science is sufficient for step 1... brs BS is just that - BS
just my $.02,
-tim
ps - do questions... lots of questions