Checking out the pitch f/x, you can see why Jackson was so highly regarded as he came up through the minors.  His fastball velocity is very nice, registering on average almost 95 mph on the gun.  His slider against RHB gets a solid 16.47% against RHB.  And, finally, he's got his BB/9 under 4.  So there are times when he can look really good if everything stays together.

vs. RHB

His problems break down very nicely when it comes to the platoon splits.  Against righties, he's got gopher ball problems.  Against lefties, it's walks that kill him.  According to the bold section header, it's time to look at the former. 

The thing is, the pitch f/x to some degree at least objects to what we see very plainly in the fangraphs splits.  His fastball only registers a .236 ISO against RHB, which isn't nearly as bad as some I've seen.  His '07 didn't feature the same substantial split, so this may well be the case of some doubles turning into HR this year.  I'd bet he's gotten at least somewhat unlucky this year vs. RHB.

His command has actually improved, at least to this side of the plate.  His balls per pitch to righties is solid and his overall figure is a tick above average thanks to his struggles finding the plate against lefties.  Plus velocity and solid command with a good slider means that RHB may struggle, particularly those who cannot recognize the slider.  Q struggles with this at times, though rarely late in the count.  JD demonstrates similar skills, so I think they'll be alright.  Farther down the lineup, we'll see some struggles, but with only two pitches against RHB, even the batters with poor recognition skills will get lucky.  His command isn't good enough to avoid mistakes all the time.

vs. LHB

The weird thing is that so far this year, his ISO against LHB with the fastball has been under .200.  Weirder still, it looks like he may be throwing a slightly modified version of his four seamer to lefties.  There's an inch and a half difference between the horizontal movement of the fastball against batters from each side of the plate.  All I have is the experience looking at quite a few of these, but I'm pretty sure that's a change in approach.  So far, it's worked well...when he's found the zone.

Jackson is fairly well below average in command with all three pitches against lefties, so I think stacking the lineup is our best chance to knock him out.  I'm not convinced that more horizontal movement would have that kind of consistent effect against LHB, for one, but for two we have plenty of right handed sock with Q! and JD.  We need Swish and Co. on base in front of them.

As for his offspeed stuff, it's pretty below average because he can't find the zone enough to make it matter.  He can't even get 5% of sliders (which he throws as frequently as the change) for called strikes.  Yet 40% are called balls.  If the slider doesn't generate a swing, it's a ball.  The change is largely the same.  Without swing and miss potential, I don't buy the relative success he's had with the pitches so far when they've been put in play.  That's, of course, sight unseen, but I think we're pretty well prepared for such a pitcher.

In Sum

Jackson looks like a closer to me.  He's got a blazing fastball and a slider that would look even better with a couple ticks on his fastball.  As it stands he's trying to become a 3, but has some work to do to get there.  I think the Rays have already done a tremendous job making him into a serviceable starter.  It remains to be seen exactly how far his still obvious potential can take him, but in the right hands and the right place he could be quite good.