Berrios looks like a pro, although the scouting projection of him topping out as a #3 are looking more likely IMO.
Mejia is frustrating. I really, really hope someone forces him to cut 25 pounds over the winter and field his position better. He has a good slider, decent velo, and that's enough to get by most of the time. He just leaves too many outs on the field due to poor fielding of his position. Cutting weight might help him go deeper as well.
I don't expect big Erv to throw multiple CGSO's in a season for the rest of his career. He's still okay, but peripherals (and age) suggest he could be nearing the beginning of the beginning of the end.
Gibson and May are complete non-factors as far as the rotation goes IMO. So they have two spots to fill in free agency, one of which I expect to be Garcia, on a 2-3 year deal probably.
They really need to go big on the other one to have a prayer. Get Otani or Darvish. It'll never happen of course, but that should be the penalty for a decade of ineptitude with developing pitching internally.