The D'Backs have acquired Adam Dunn for three players. One of them is minor leaguer Dallas Buck, who's a decent prospect who was in the rotation for Class A+ Visalia. He recently had Tommy John surgery but has pitched acceptably since returning. The others are players to be named.
If Buck is the key player the Diamondbacks are giving up, this is a great move for them, although it's unclear to me how they'll align their outfield. With Justin Upton out, Arizona's real problem is that they've got Alex Romero starting most of the time in right field. Neither Dunn nor Conor Jackson have played any right field this year, so I'm not sure who will start there, or if Dunn will replace Romero or maybe first baseman Chad Tracy. Either way, this gives Arizona a much better shot at staying ahead of the Dodgers and winning the NL West.