Against RHB he's basically death. His fastball, which he throws on average harder than 94 mph, is basically a sinker, with batters posting just a .167 ISO against. I think the primary cause of this is the ton of ride he gets, with more than 7 inches of break horizontally (a lot for that kind of fastball, in my experience writing these) His curve has a well above average whiffs per pitch rate and he gives up .185 ISO. He doesn't throw it for a strike that often relative to the average, but he gets so many whiffs out of the zone and throws it primarily once he's ahead, so the cost of a ball is lower anyway. In any case, there's no real evidence that he struggles with curve command. And he pounds the zone with his fastball so effectively that working behind in the count does not work against him like the average pitcher.
The change is an opportunity, but I couldn't detect a usage pattern, so actually being able to make something of it requires acute recognition from the batter. The other interesting note about the change is that he throws it almost exclusively inside to right handers. That's strange, but it suggests that he's really trying to sell it as a fastball and doesn't like to let righties really see it (longer plane to throw across the plate-->more time to examine pitch). So, while he gets a solid whiff rate, it's a matter of his approach rather than pure stuff. The .471 ISO against backs that conclusion. It's an opportunity but making something of it is still difficult.
He's had a terrible time throwing strikes to LHB this year and he has at least some history of trouble. According to his BP card, his L/R splits:
The difference in power hasn't shown up so far this year, as his change up is profiling divergently in this regard from righty to lefty. This makes sense to some degree. The inside changes to righties that get mashed when recognized are away to lefties. If you remember the fastball dot graphs I posted from John Walsh a while back, it's much harder to hit the pitch away for power. It's strange that pitches Verlander has little trouble spotting against righties become so much more difficult against lefties, particularly since his inside spots to RHB should translate just fine to LHB. It looks to me like there's a mental block there.
Neither RHB nor LHB will have an easy time today, but if Sox lefties can take the walks that Verlander has been handing out thus far, their chances look much better. And, clearly, there's a reason why Ozzie is stacking his lefties in this lineup. Let's remember this next time we call Ozzie out for being stupid. This is just one point of many in his favor. He's been outstanding this year.