Jackson has an electric arm and is able to hold his velocity for 100 pitches, touching 97 or 98 late in the game and sitting in the mid-90s. His hard slider has good tilt with a break that starts early and deepens as the ball travels; he also flashes a below-average breaking ball.
His arm is quick, but there's some effort in the delivery. It's top-of-the-rotation stuff, but Jackson simply does not command either the fastball or the slider, and hitters make far too much contact given the quality of his two main pitches. After two mediocre-to-bad years as a starter, Jackson probably is due for a shot in the bullpen, where Detroit is deficient and manager Jim Leyland has had a lot of success with pitchers who have failed elsewhere.
Joyce profiles as at least a part-time outfielder who needs a caddie against left-handed pitchers but who hits against right-handed pitchers very well and could be part of a very productive and cheap corner-outfield platoon.
Joyce's best attribute as a hitter is his sneaky raw power, as he's not a big guy but has above-average pull power; he could hit 20-plus homers if given enough playing time. He takes a big cut and will swing and miss on his fair share of pitches, leading to inordinate hand-wringing over his strikeouts, but he works the count enough to post an acceptable on-base percentage from the left side.
Joyce is not futile against left-handers, but he's at enough of a disadvantage that a right-handed platoon mate is probably called for. He should be part of a two-headed right-field monster for the Rays, who have shown an ability to find productive yet cost-effective solutions when they don't have the cash available to play in the free-agent market.