Pretty bad. From AZ Snakepit's Jim McLennan, a list of the five worst seasons in franchise history, with our retiring hero not far from the top of the list:

3. Melvin Mora: 2011, 520 OPS (.228/.244/.276, 135 PA)
In contrast to the back-ups that represent most on this last, Mora was a good deal more expensive earning $2.35 million for his "efforts" last season. Things started badly, as he went 0-for-5 with two GIDPs and a WP of -45.3% on Opening Day, a figure never close to matched by a D-back the rest of the year. Mora's complete lack of power or plate discipline were obvious problems. He hit nothing more than a double, and his 135 PAs was the most by a player in a season with two or less walks, since Rafael Belliard had 148 and two BB for the 1996 Braves. Yeah, in hindsight, this signing should have been strangled at birth.

Granted, it's hard to go wrong with $2.35 million. But the Diamondbacks did. Give them credit, at least for cutting Mora before he could do any more damage.

It was a sorry end to a pretty good career.