Overall, there are no really grating voices in the dub AT ALL.
Black Star, the main offender in the first four episodes, starts to sound better during the Masamune arc.
Crona is the one I am most iffy about. It's a good fit, but still she doesn't sound insane enough.
On the subject of Crona, the dub goes with 'him'. :\ HOWEVER, this is addressed in the Episode 7 commentary!
Ragnarok sounds a little off at times, and then degenerates into a near replica of Usopp when stressed, but overall I couldn't tell it was Sonny Strait until he started sounding like Usopp.
Medusa is a PERFECT fit. Seeing how Nami was the first (and up until now, only) role I've seen Luci Christian in, I was hard-pressed to actually HEAR "Nami" in the delivery, which showcases the actress's range. :P
Excalibur is pretty funny, but not overly annoying
Masamune = Kyle-fucking-Hebert! use your imagination from there. (Nah, seriously, it sounds like a rougher Cobra)
Stein goes from fitting to slightly annoying at times, but still a good fit.
Overall it's an excellent dub. The only annoying voices before were Black Star, Kid, Liz, and Sid. But the first three are very fitting in the grand scope of the series whereas Sid just grows on you. Overall, I'd rate the dub very highly, but behind One Piece a bit.