I sent the current draft of book 1 out to several beta readers, with the instructions to take their time reading and get back to me if/when they had input.
My father (who received a PG-13 version of the manuscript, because I would die of embarrassment if he gave me feedback on my sex scenes) mentioned a factual error, and had two lines he'd written down. The first was because he tripped over it while reading (there are three prepositions in the sentence), but then it grew on him and he wanted me to keep it. The second was because I'd described something in a way he'd experienced, but never thought of using those words to capture it.
The second person emailed me to say that she started reading it on Tuesday (when her work break started), and she tried to stretch it out to dole out feedback, she really did, but she couldn't put it down. She finished it yesterday, and emailed me to say she liked it a lot. She wanted to know if there were more books, and I assured her that, yes, there will be two more before the story is done.
The second reader I picked because she reads a lot of urban fantasy and, while our tastes don't always mesh, she's good at picking out what she didn't like about a book or expressing where a book lost her interest.
I still have two other beta readers and a crit partner to get feedback from, but so far, I'm pleased with the results.