Starts out excruciatingly slow, and is marred by poor editing (Is the school headmaster Mr Tuffett or Ms Muffett?) It picks itself up a bit in the final third and becomes a nice but somewhat uninspiring read.
Others have mentioned how their biggest disappointment is the relegation of Atticus from God Almighty to Regular Joe. I don't see that at all. All through Mockingbird I looked at Atticus as a decent role model for fathers and people in general, but felt very clearly that he was presented through the eyes of a child that adored him. This book only strengthens that view for me. Atticus is still as much a standout father, but with the obvious flaws that make him a mortal man. His handling of what can only be called a very delayed teenage rebellion seems to me to be nothing but a success. That he has views and opinions most people today probably do not have takes nothing away from that.
I went into this with low expectations, I figured there was a good reason this book was never published, before and there is. It appears unfinished and rather immature and would probably not have appeared at all (or at least not in this form) had it not been a guaranteed success. In conclusion, you certainly do not _have_ to read this, but it's not all bad either.