The Rangers signed Leonys Martin to a 5 years 15.5 million contract back in May of 2011. He played 29 games in AA and had a .435 OBP, but that dropped significantly in AAA, where he had a .316 OBP (and .630 OPS in the hitter friendly PCL). Neither of these sample sizes are particularly helpful.
In his last 3 years in Cuba (his 3 seasons with more than 200 AB) Martin batted .345/.477/.518. Clay Davenport projects 263/.339/.399 and a 2.1 WAR for Martin in 2012. Davenport also has a Yeonis Cespedes projection, where he turns his Cuban numbers of .333/.434/.667 into .251/.309/.451. This is a .082/.125/.216 regression. This turns Martin into a .263/.352/.392, so really close.
Davenport also says that Cuban baseball can be graded like "low A ball." According to this (and our A metric): Martin projects to be a .428 OBP and .451 SLG (.879 OPS). This is nowhere close to Davenport's own projections, which means our A-ball projection is not helpful for Cuban statistics.
So Martin seems to be a guy with an average batting average, solid OBP, and under average slugger with .744 OPS. This is a 1.52 Simple WAR. According to Runs Created formula, Martin is projected to create about 82 runs in 140 games, or 17 runs more than an average hitter. Defensively, Martin had a 2.45 Range Factor per Game in the minors. 2.59 Range Factor per Game is about league average for center fielders. This means that Martin will get to almost 20 less balls than an average center fielder. If we assume that each time Martin doesn't get to a ball that an average fielder would get, he cost his team one base, or about 5 runs overall if he plays 140 games. This still leaves him responsible for 12 positive runs more than an average player would.
To be worth his contract, he really needs to be about league average, or provide 5 wins over replacement in his 5 years. According to Davenport's WAR projection, he will be worth over the about 3 million dollars a year. So it seems according to the projections and all metrics, Martin will be worth the contract the Rangers gave him in 2011. Now to see if this actually becomes the case.