He looks a little big (stocky), slow, and awkward at 3rd base.I have seen questions about whether he will stick at 3rd base or not, and I can see why. He doesn't seem to move well, as stated, and his hands (something I don't really talk about that often) seem to "not be soft". The ball seems to clank off his glove and hands a lot. Whether this is just general clumsiness that comes with being young and continuing to learn or a "natural ability" remains to be seen (I at least lean with the former. That doesn't mean he will learn, it just means I think he can with practice).
There are 7 MLB 3rd baseman that had enough qualified innings and a positive UZR (which at least gives us a ballpark estimate of whether they are good or not defensively) in 2012. Their heights are as follows: 6-0, 6-0, 5-11, 6-1, 5-9, 6-0, 6-2. Listed anywhere between 5-11 to 6-1, Cuthbert certainly falls under that umbrella. He is listed at 190 pounds, which would be smaller than any of the 7 (215, 210, 220, 205,200, 215, 200). The listed weight is most likely conservative, but it doesn't seem that he is necessarily too big to play 3rd. The question is whether or not he will continue to get bigger.
At the plate, he has a fake strike where he brings his leg and foot up (but not out, so no stride) only to put it down before the ball gets there and starts his swing. This is usually not a positive, but the swing and bat control both seem to be solid. He can go get low pitches and seems to have the ability to handle high pitches. Probably more of a line drive guy right now, but you could see Culbert develop a little bit of power, and there does seem to be a slight (not big) uppercut in his swing. Breaking balls seem to get him out of his element and his swing, or at least from what I have seen.
Culbert is not very fast when it comes to foot speed, which seems to match what I saw out in the field. He runs about a 4.45 (I got 4.47 and 4.48 on 2 separate tries of the same "dig") to first base. The average Speed Score of the 3rd Baseman above was 3.9, so there may be some complaints that he isn't athletic enough to play third, which certainly looks to be the case, but Adrian Beltre and Alberto Callaspo actually have slightly worse Speed Scores.
I think he was usually rated above Adalberto Mondesi, but I would probably rank Mondesi higher (even though he is further away from the big leagues). This picture may give you a look as to why (other than just the general athleticism and more rounded game Mondesi has):
Adalberto Mondesi: League Average Age: 20.8. Age: 16.92 (3.88 years younger). Speed Score: 7.2 (4.10 to first). Hitting: 95 wOBA +, 90 OPS +, 90 wRC + (.410 BABIP)
Cuthbert: League Average Age: 22.5. Age: 19.58 (2.92 years younger). Speed Score: 2.9.
Hitting: 89 wOBA +, 74 OPS +, 73 wRC + (.276 BABIP)
It seems pretty clear that Mondesi is better (especially once you factor in that Mondesi plays the middle infield while it doesn't seem that Cuthbert sticks at 3rd), the main counter argument being BABIP. I think Mondesi caught a lot of people by surprise by how well he played this year (reports from the off-season suggested he was still pretty raw), and my guess would be that in this year's rankings he will be consistently higher than Cuthbert (obviously my comparison is in full hindsight and in no way a critique of anyone's prospect ratings).
Matthew Minton of "Seedlings to Stars" wrote in the middle of the season as Cuthbert was really scuffling at the plate:
"I think a good rule of thumb here with Cuthbert is that if you liked him after the 2011 season, there’s really no less reason to like him now."And I agree. He was basically too young for the league he was playing in and his K/BB still wasn't bad (it wasn't as good as Bogaerts, but it was better than Odubel Herrera's and Trayce Thompson's), suggesting he wasn't totally overwhelmed. There are some things he needs to clean up in his approach and swing, but he looks like a guy who could be a good big league hitter. His future may be in the corner outfield, but there is a chance that he could hit enough to make up for it. Expect him to repeat A +, but I would expect him to have more success and be closer to league average (if not league average) in 2013.