He's a fine enough team defender, but certainly nothing close to a stopper on defense. Slightly below-average probably?
What he is elite at is shooting and he's an excellent secondary creator/ball-handler. It's a pretty similar pick-up to Monk in a lot of ways where he'll be an awesome fit with Fox/Sabonis and gives more passing/ball-handling.
I love he's locked up long-term, going to be 24 by season's start and directly on the timeline of everyone else in the core. Murray, Huerter, Monk is a HELL of an offensive upgrade to what we had last season.