I wonder, as a wrestler your head don't really get 'rocked' (by punches) the way boxers have to get used to. It seems he didn't know what to do when that happened. So it could be an experience issue there.
As for skill: Valasquez connected with 48 of his 59 punches. Looks like Lesnar has a pretty serious weakness when it comes to striking. People who are more familiar with BJJ, can you answer this question: how technical is Brock's ground game? He seems to have no problem getting Valasquez down, but when Valasquez countered his submission attempts, he didn't seem to be able to change/counter. So that made it look like Valasquez got free rather easily each time.
I've been watching the Lesnar-Valasquez previews the last couple of weeks. The way UFC portrayed Lesnar, he was the second coming of Beowulf. So it was really disappointing that while Valasquez had a great performance, Lesnar had a very poor one.