I just literally wrote a response to this Latos trade in the last hour with all these great stats and stuff, and I go to post it, and it doesn't go through because of my shitty internet. Kind of pissed. Going to quickly recap, as I'm too lazy to look up everything again. Go to baseball reference if you don't believe me.
To recap what I tried to write, the Reds need SP because their offense is good as it stands with Votto, Phillips, Stubbs, Bruce, etc. Latos provides a great upgrade from Volquez, as Volquez has missed some time in the last 3 years. Latos is also 24 and has better a significantly better IP, ERA, WHIP, WAR and SO/BB than Volquez. Latos also has a slightly above average Adj. ERA+ while Volquez is below average. Though Latos will obviously preform worse away from PETCO, he will still pitch better than a average pitcher. (If you didn't know, Adj. ERA+ adjusts ERA to the players ballpark for better comparison of pitchers in a hitter friendly parks to pitcher friendly parks). Latos is also only entering his third full season and has far more control at a lot cheaper salary than Volquez.
The prospects that the Reds gave up were practically a junk pile. They gave up a minor league reliever with control problems, a 1B prospect that is blocked by Votto, and one of their many good catching prospects. In return, the unloaded about $1.3 million in unneeded salary and gained a potential superstar pitcher with proven big league success. The Padres lost this deal, as they don't really need Volquez and the biggest prospect that they got is blocked by Rizzo at 1B. They honestly should have asked for Leake to at least have some upside. Overall, a major win for Cincinati.