He mainly played left-field in the Cuban Serie Nacional, with some center and right. According to Clay Davenport's ratings, he was below average defensively. His speed was also rated slightly below average according Davenport's formula. If you use traditional speed score ratings, Alvarez obviously rates below average with 13 steals over 5 seasons, with 21 caught stealings. Reports do seem to say that he has an above average arm, which may help him profile in right-field.
With the bat, when he first jumped into the league, he predictably struggled at age 19. He got incrementally better each year offensively until his last year in 2011 where he would hit .363/.404/.613. According to Clay Davenport's projections (which basically treats the CSN like A-ball), that year projects to a .303/.327/.494 season. If the statistics I am seeing are correct, he has insanely low walk and strikeout rates, and his 2011 would translate to just 12 walks and 33 strikeouts over 611 at-bats (when you include the previous years, there are many more strikeouts). This is something you would normally see in a slap hitting middle infielder, not a corner outfielder. It seems that Davenport conservatively projected Yeonis Cespedes in 2012, as he was a 3 win player in 2012 with the A's, with a .356 OBP and .505 SLG. Davenport had both his OBP and SLG lower by about .050 each. Cespedes did have a somewhat high BABIP, but he also played in a pretty pitcher friendly park (and as far as I know, the Davenport projection was neutralized, not taking into account Oakland's ballpark), so one could say those roughly even out. If you still want to neutralize the BABIP, assuming that Cespedes is not a naturally high BABIP player, and see how Cespedes would have hit with a .300 BABIP, we get a .260 batting average with a .324 OBP. This is still a little better than league average (and doesn't factor in his above average power), and still about .010 points of batting average higher than Davenport projected and nearly .025 points of OBP better. He walked a little more than expected, but he also hit for a slightly higher batting average. Now, it would most likely be foolish to just add those extra points onto Alvarez' projection, or even to scrap Davenport's projections altogether. Instead, lets look at the differences statistically between Cespedes and Alvarez. While Alvarez had solid but low K/BBs, Cespedes actually walked more than he struck out the last three years he was in Cuba (and he was criticized, by me as well, for his plate discipline). Cespedes pretty consistently hit for more power than Alvarez as well, though Alvarez' SLG in 2011 was very comparable to Cespedes' last three seasons. Defensively, Cespedes' was ranked as a very solid defender (with a couple of really awesome seasons) by Davenport, but UZR, DRS, and FRAA all thought he was below average defensively in the Majors. From just personal observations from watching Cespedes throughout the year, it seemed he had enough athleticism to be a good defender, but really struggled with jumps and reads (though it seems that he did get better throughout the year). If Cespedes was rated positively by Davenport then negatively by the traditional defensive metrics when with the Athletics, it is probably not to much of a leap to assume that Alvarez will be rated very poorly as a defender in the MLB.
From watching video of Alvarez, it is clear that he has a large and somewhat violent stride to start his swing. He holds his bat up high and seems to uppercut his swing. The bat seems plenty quick and he seems to have good control of it (note that most of what I saw was just batting practice).
His lack of apparent tools and positional value makes it imperative that he really hits. While for some reason I was under the impression that offensive statistics took a big jump from 2010 to 2011 in Cuba, this doesn't actually seem to be the case. So, at least statistically, there seems to be reason to believe that Alvarez has developed as he has aged and that his last year in Cuba was at least somewhat real. Using Davenport's methods, he would be an above average hitters in the Majors, with a low walk rate, but good average and power. This might be enough to make up for a lack of speed or defense and have him as a traditional corner outfielder with a big arm and big power. I thought somewhat of Nelson Cruz as a lazy comp, but if you only look at Cruz' road numbers (neutralizing the Ballpark in Arlington factor), Alvarez projects as a better hitter. While his mechanics as described above aren't necessarily pretty or perfect, he has the bat speed in my opinion, and could be a legitimate big league starter.