When he is on the field, he is arguably one of the best hitters in baseball. He just hasn't been on the field very often as of late.
2014 Statistics: .283/.369/.448 (135 wRC+), 13 HR, 3.4 fWAR, 2.7 WARP
2015 Age: 31
2015 Position: Shortstop
Hanley Ramirez is easily, by true talent at least, the best offensive infielder on the market this winter. At a career mark of 133 wRC+, only Alex Rodriguez has been a better hitter at shortstop (kind of) in the past 20 years. The Yankees have been in dire need of an impact right-handed bat in their lineup for the past couple of years, and Ramirez fits the bill to a T. The only problem is, though, that he can't be relied upon to play every day or to play shortstop for his entire contract, however long that may be.
In 2013 we saw how talented Ramirez could be. In 86 games he hit an absolutely ridiculous .442 wOBA (and 5 fWAR!), which is basically a Babe Ruth-esque level of play in limited time. But of course, 86 games sticks out. If the Yankees are going to invest in a long term solution for the infield, then it can't be someone who can only play for half of the season. Sure, a half season of what he did in 2013 combined with Brendan Ryan is still great, but I doubt he performs like that past his age 32 season. In the past couple of seasons he's had a torn ligament in his thumb, and numerous strains in his calf, hamstring, and oblique. These types of nagging injuries only get worse with age, and the Yankees do not have the infield flexibility to deal with these injuries should they (they will) arise.
There's also the question of defense and positioning. Depending on which defensive measure you use, Ramirez is either pretty bad or terrible as a defensive shortstop. He's about -8.8 UZR/150 for his career or -78.9 FRAA. Either way, this is going to get much worse. Ramirez will certainly be so dreadful defensively that he will be forced to third base or DH for the last few years of his contract, and I'm sure the Yankees will have a number of older guys vying for those positions.
If we put those all together, we get a potentially great offensive player with poor defense and a sketchy injury history. That's not exactly easy to parse, and it's especially complicated if you are the Yankees' front office. The Yankees are now knee deep in expensive contracts after yet another failed run at the postseason. This mediocrity looks to continue in 2015, and this time without a retirement tour boost. When Ramirez is healthy, he is an amazing player that will greatly increase the team's odds of making the playoffs. But if they once again fail and the plan implodes, then we're looking at yet another mess of a contract.
The next few years could be a watershed moment for the future of the organization. The team has quite a few contracts expiring (including Brian Cashman's!) in a few years, and that could be a great opportunity to reset if they need to. But if they commit to yet another lengthy deal that fails, then it could be the straw that breaks the camel's back. They need to be absolutely sure that he will be good for a few years, and I don't know if that's clear.
If I'm the front office, I pass on this. This just screams of a bad contract waiting to happen, unless his stock has fallen so low that he can be had for a fair price and fewer years. Because that's unlikely, I think it'd be best that the Yankees focus on players that can act as stopgaps for the next few years. With a few more excellent seasons, Ramirez is nearly Hall of Fame caliber. But he's also a bad injury or a few bad years away from becoming Nomar Garciaparra after 30, so there's that, too. If the Yankees want to pursue him, it'd be best to tread cautiously.