WARNING: The following post contains spoilers for A Feast for Crows and A Dance With Dragons from the A Song of Ice and Fire series by George R.R. Martin. If you would like to remain unspoiled, you should recuse yourself immediately. If however, you've read the series, are familiar with the endings of both AFFC & ADWD, or don't fancy reading it at some point in your life (a true mistake IMHO) you may read on.
THE SHORT VERSION
It's not too complicated: A Feast for Crows, while shorter, definitely reads slower but is not less enjoyable. You'll appreciate the storylines of Cersei, Arya, and Brienne, but get a bit angry/annoyed at Samwell, Jaime and the massive cast of Greyjoys. Not my favorite in the series, but I wouldn't call it the worst in the series (if there even is a worst) which is apparently the popular opinion.
As for A Dance with Dragons, it's by far my favorite book in the series. I couldn't put it down - it was a rollercoaster of emotions! A bit slow to start, but holy moly once it gets going it's hard to stop reading. I cheered for all of my favorite characters and changed my mind about a few others. It also provides A LOT of much needed backstory and explains/confirms more than I think all of the other books. If A Game of Thrones is your gateway drug, this confirms you're an A Song of Ice and Fire addict.
For the much lengthier, much more passionate review of the final two books in ASOIAF, I'll see you after the jump.