Matt Cain is one of the more reliable litmus tests for Giants-related optimism. If you're excited about San Francisco's chances in the NL West, you probably have Cain down for an ERA in the threes. If you think the team is going to flounder, the projected struggles of an overextended rookie are likely a big part of the problem. Point and Counterpoint are working things out, so we'll go to the Good, the Bad, and the Ugly:
The Bad: A lot of his success as a Giant was due to a ridiculously low number of hits allowed. That kind of hit rate was likely a fluke.
The Good: There were a couple of starts where Cain featured little more than a fastball, and the hitters still weren't comfortable.
The Bad: The breaking pitches were inconsistent, with the true bite of his best breaking pitch a rare sight.
The Good: There isn't a bad thing to be said about him, as far as the scouts are concerned. The stuff's there, the makeup's good, and there isn't too much pressure on him at the back of a rotation.
The Bad: That wacky walk rate, which is a frustrating thing to watch a young pitcher overcome. Shawn Estes, Russ Ortiz, and Joe Nathan all had control issues when they were first inserted to the rotation, and only Nathan was able to fight through the control struggles for his career. Apples (Ortiz, Nathan), oranges (Cain), and Corn Flakes (Estes), to be sure, but high walk rates are usually one of the biggest obstacles for young pitchers.
The Ugly: Randy Johnson.