Myers has shifted back and forth between the bullpen and the rotation several times in his career. After starting in his first four seasons with the Phillies, he was moved to the bullpen in 2007, then moved back to the rotation in 2008. And after two seasons in the rotation with the Astros, he was moved to the bullpen this past year, with success. The impression I get is that Myers can either be decent innings eater or a good reliever, depending on your team needs. From Myers' standpoint, though, the rotation was where he wanted to be, for a decent starter is going to get more money on the market than a good reliever.
Hence the deal with the Indians. The Indians by most measures had the worst starting pitching in majors last year, and with a very good bullpen, would be less likely than most other teams to move Myers to the bullpen. Assuming he makes the rotation, Myers would allow the Indians to option both Trevor Bauer and Corey Kluber to AAA to start the season, with Bauer going to AAA for "seasoning" and Kluber to serve as depth.
Myers' best pitch is his curve, though that has made him homer-prone in the past; in 2011, he allowed 31 home runs in 216 innings, and that wasn't really a career anomaly. I wouldn't expect Myers to be much more than an innings eater, especially in the American League, but with the Indians' starting woes, an innings-eater is an upgrade to this rotation. Once upon a time he was a power starting pitcher, but those days are gone; I'd expect an upper 80s fastball, and a non-zero chance of being a bust with the move to the DH league. The risk from the Indians' standpoint isn't all that great, though, because they could always move him to the bullpen if he doesn't work out in the rotation.
Myers' personality and past off-field incidents need to be mentioned. Early in his career he had a rather volatile on-field personality, though as he's gotten older he seems to have mellowed out. In 2006, he was arrested for assault after witnesses say he hit his wife in public. The case was later dismissed after Myers' wife requested that she did not want the charges pursued.