Why the Rockies took him:
The Rockies are starting to show a strategy of college strike throwers with this last pick, with Moll dazzling scouts with plus stuff and only 2 walks on the Cape last season. He is not exactly the best player available, but Rockies Pitching Coordinator Mark Wiley wants a certain type of guy, and Moll gives them hard, strikeout stuff, and generally good command, albeit from a pint-sized frame.
Why you should be excited
If he wasn't 5'11", Moll might have had looks as a first rounder. A lefty pitching at 92-94 while flashing 96 with cut or tail has a 60 present fastball. His curve-now-slider has hard 1-7 break, and could also be a 60 pitch with work. Moll is athletic, repeats his delivery, and has improved his control every step of the way.
Why you should be worried
He's 5'11", meaning he has to maintain command down in the zone or he will be home run-prone. Moll's control has deserted him in the past, but he's cleaned that up recently too. Ideally, you are hoping he can start, but Moll has used his change too infrequently and may end up a two pitch reliever, yet not quite closer/eighth inning good. Durability at his size will always be a concern.
What needs to happen for Moll to reach the majors
Assuming they start him, Moll has got to develop his change, and being athletic with a repeatable delivery, you can hope for it. Can he throw his hard stuff for six innings every fifth day? Durability and arm resiliency will need to be monitored.
Realistic best case scenario
Moll has similarities to Tyler Chatwood and thus probably has the same ceiling, though from the left side. He could be a #3-5 starter with strikeout potential, but he would probably be more a 185 inning guy.
Wiley's already working to remake the system with three college arms that throw strikes with 60 or better fastballs, Moll may not have the physicality, but the stuff still impresses.
You can follow Sam Moll on twitter here.