His body of work this year is quite small and his mechanics are a work in progress, having said that here goes ...
Fastball - sits 91-92. Occasionally hits 93 or 94, more often hits 88-90. Fairly flat with no jump at the end and no big movement either. But hides it well and it appears a couple mph faster. And something that functions as a flat 94mph from a leftie is nothing to sneeze at. Locates it well and down in the zone.
Curve - 78mph with more of a slurve action. As season wore on less slurve action. I'll get to that more under mechanics. Seemed to locate it fairly well in the zone. The slurve type did get hit more than it should unless it was well out of the zone. I think it's a quality pitch because of the location and his willingness to come inside.
Change - Count me unimpressed. Their scouting director loved Matusz and said he had the best curve and change in the draft. Maybe that was because it was a pitching weak draft. But his change has very little movement. Yeah he can locate it but that's because it's fairly flat. At least it is deceptive, but watch out when facing hitters looking for the change.
Slider - Doesn't have that much action. I do like how he isn't afraid to ride it in on the hands of righties. If he does get some real action he won't be able to do this though, either too many HBP or bounced pitches will occur. I've heard average to plus - from within the organization, and show-me pitch from others. I'd lean somewhere in the middle. It doesn't have that much to it but it's consistent and he knows when and where to throw it.
Mechanics - I try to keep away from this and probably will in the future. Partially because I'm lazy. Ok, mostly. But also many pitchers really don't make drastic changes and it's so hard to predict.
Matusz was more of a 3/4 pitcher and Baltimore has been changing this. You can see in just about any game his delivery is somewhat erratic as he occasionally reverts to his old arm slot. The slurve versus the more downward curve is the most obvious. As he gets used to this I expect his control to get better.
He doesn't get much separation and is a part of the reason you don't see as much velocity as he could get. Another is his awkward stiff landing and release. Watch the video below and focus on Kershaw. Notice how Kershaw lands fairly softly on his lead leg and only after landing does he unleash - getting extra power and using the leg to stabilize. Of course on the video you will see Matusz hiding the ball very well. As he gets more upright will that go away? Maybe a little, but with the apparent late hand break I think not.
Prognosis - I really like his locating the fastball low and the late hand break hides the ball well. I like how he works his pitches, coming inside on non-traditional pitches. My big concern is to righties where his change is flat and his curve is either slurvy (great on 0-2 counts) or not that hard breaking but better location.
I think he will be a solid pitcher and can be a #3 with a high 3 ERA. And more likely will have more of his career as a #4.I like pitchability. But when your location is off or one pitch can't be located then he will get lit up. Aces and #2's have to put up solid numbers in half a dozen games or more where they don't have their best stuff.
If his mechanics change to get the velocity he has in his arm then all bets are off.
Mechanics video (Courtesy of Baseball Intellect)