Keith Law filed his report after yesterday here:
You have to be insider to get it, but if you are, enjoy. If not, a brief snippet:
There are big-league starters who look like they're playing catch when they pitch, like Livan Hernandez; there are almost no big-league pitchers who look like they're playing catch at 96 or 98 mph. But Chapman does. His arm is loose and quick, and he makes a relatively easy thrower like Steven Strasburg look high-effort by comparison.
In terms of mechanics, Chapman takes an enormous stride towards the plate and pronates his arm reasonably early; the arm path isn't long and there's no violence or other major red flags in the delivery. If he stays healthy, he's a number-one starter, and should be able to come north with the Reds in some role this year if they want him on the big-league roster.
He described the slider as absolutely toxic, with a sharp break and sitting at 87-90, or what a normal left-hander sends plateward for a fastball. He raved in general about the ease of the delivery.