The Mets get Johan Santana without giving up Fernando Martinez, their best prospect, or Mike Pelfrey, their best young pitcher. They also immediately make themselves the favorites to win their division and have a good argument that they're the best team in the National League. It's hard to see this deal as anything other than a win for New York, and given how many people claimed (erroneously) that the Mets didn't have the prospects to get Santana, it must be doubly sweet for Omar Minaya right now.
For the Twins, or at least for their fans, this has to feel like a huge letdown after a winter that saw names like Jacoby Ellsbury and Phil Hughes bandied about by the media, although whether those players were actually available in trade talks is another matter entirely. The Twins deal their best asset and the best pitcher in franchise history -- not to mention the greatest Rule 5 pick in the history of that draft -- for quantity, but not the type of quality you expect a pitcher of his caliber to fetch in return.
In Santana, the Mets get one of the game's best pitchers, a two-time Cy Young Award winner who has to be the early favorite for the NL Cy right away, given his track record and the run and defensive support he'll get in New York. It's a five-win upgrade at worst, more if you consider the sixth- and seventh-starter types the Mets might have had to employ this year had they not made this deal. But the addition of Santana does two things for the Mets above and beyond the direct value he provides with his pitching. One, he'll give the Mets 50-75 more innings than they would have gotten from the starter he replaces in the rotation; he takes pressure off their bullpen and allows Willie Randolph to give his best relievers more rest, which he wasn't able to do last August and September. Two, he pushes everyone in the rotation back into a more suitable spot. Pelfrey now has to "win" a starting role in spring training, which, given the work he still needs to do, is not a bad situation. Oliver Perez and John Maine won't line up quite as often against opposing No. 1 and 2 starters.
Santana is not without his red flags; he stumbled to the finish in 2007 and in the past has had elbow chips, a problem that tends to recur. He's become more flyball-oriented recently, leading to a big spike in his home run rate this year; the acquisition could encourage the Citi Field architects to push the fences back a few feet. And the days of him shouldering 230-240 innings a year may be behind him, although facing the pitcher two or three times a game may help him recover some of the lost workload.
The Twins' package includes two raw prospects with high ceilings and two near-in, low-upside arms. Carlos Gomez is a plus-plus runner, has a quick bat and makes a lot of contact with a wrist-heavy swing, but doesn't project to hit for power now because he doesn't use his lower half to get more power into his swing. He's an excellent defender in center with a plus arm -- imagine a Coco Crisp who could throw the ball to the catcher without 15 hops -- which may encourage the Twins to use him in the majors right now, even though his bat's not ready.
Deolis Guerra is almost all youth and projection at this point, with his one major current skill an above-average changeup. His velocity is fringe-average and wildly inconsistent within outings, so the optimistic projection is that he'll eventually sit 92+, but there's also a good chance that he settles in where he is now. His curve has some depth, but like his velocity is inconsistent, and his feel for the pitch is particularly poor. He has a great pitcher's frame, 6-foot-5 with very broad shoulders and lots of room to fill out, and the fact that he has an advanced secondary pitch bodes well for him improving his command and feel with experience. But the bottom line is that he's 18 years old, so in the best-case scenario, he'll be contributing in the majors in three or four years, and that's if he doesn't get hurt or hit a snag in his development.
The other two arms are major-league ready or close to it, but have limited upside. Philip Humber's curveball was once a big-league out pitch, but since Tommy John surgery, it hasn't been as tight and he hasn't commanded it as well, leaving him more reliant on his average fastball to get hitters out. He has good control and an average third pitch in his changeup, but his days of upside as a No. 2 starter are gone. Kevin Mulvey also has a three-pitch repertoire but lacks any kind of out pitch, making up for it with good command and a willingness to mix his pitches up to get hitters out. Humber has a chance to break out of the 4/5 pitcher group in Minnesota, which also includes Glen Perkins and Kevin Slowey, while Mulvey just gives them another cheap option if one of those guys isn't ready in April.
In the abstract, it's hard to accept dealing your marquee player and top trading asset without getting your partner's top young player in return, and that's what the Twins did. They did get back significant economic value in four young players, each of whom has under one year of big-league service and two of whom aren't even on the Mets' 40-man roster yet, so the Twins will have each of them under control for six full years of service. That return in exchange for just one year of Santana's services is reasonable. But premium players should fetch premium prices, because there's value to a club in having so much production coming from a single roster spot. And in this case, Minnesota GM Bill Smith did not get a premium prospect in return.