I know it's always a little unfair to judge a trade in the hindsight of the following season, but it's naive to think that the trade isn't still affecting the Giants.
Here we are in 2012 and to nobody's surprise, offense is still in high demand and short supply, except this time there aren't any highly-valued trade chips. No instead Zach Wheeler, the talented pitching prospect who was widely considered our best prospect in the minors in 2011, is with the Mets dominating the Eastern League and Beltran is with the Cardinals dominating the National League.
The Giants meanwhile got nothing, not even a compensatory draft pick, and boy does it hurt.
In reassessing the trade, there a couple of stances you could have on judging its success or not. The kindest assessment is that it was a good trade and a good plan trading a top prospect for a big help getting to the playoffs, but the Giants just got unlucky with Beltran's almost immediate injury.
This is somewhat fair as the Giants very well could have gotten to the postseason with a healthy August full of Beltran and if that had happened, nobody would be complaining.
The other stance you could have is that the Giants made the right move in trading for Beltran, but screwed up when they failed to sign him over the offseason. At $26 million over two years, Beltran signed for slightly more than Aubrey Huff did before 2011 (fun fact: according to fangraphs WAR, Beltran has already been worth 2.8 more WAR in his two year deal than Huff's and he's only played 35 games).
Considering Beltran's enormous talent, this was a modest deal even before Beltran's ridiculously hot start and with the clause in his Mets contract that made him ineligible for arbitration (which would mean that he couldn't be a Type A/B free agent, meaning no compensatory draft pick if he signs with another team), the only way the Giants were going to retain any value from the trade after the 2011 season was by resigning Beltran.
What should the Giants have done differently about the Beltran/Wheeler trade?
You could also say that the trade was a bad idea from the start and the Giants shouldn't have traded Wheeler, as the trade essentially decimated the team's pitching depth.
Given Surkamp's injury to start the season, a top-tier pitching prospect would be incredibly valuable to the Giants right now and even more so in two years when Lincecum, Vogelsong and presumably Zito will be up for free agency. Considering Wheeler's enormous success since being traded, this is also a very viable stance, despite the Giants offensive dearth in last year's playoff race.
And finally, you could say that the trade was a good idea, but it was after the wrong guy. Instead of getting a two (hopefully three) month rental, the Giants could have packaged Wheeler and/or a few other middling prospects to nab a quality position player who was under contract for a few more seasons. This is, of course, what the Phillies did when they nabbed Hunter Pence for a generous package of four players including two top prospects in Jonathan Singleton and Jarred Cosart.
I don't think that the Giants really had the minor league depth to be comfortable with that quality of package, but a similar sort of deal for a player like B.J. Upton or Alexi Ramirez would have at least ensured that the Giants at least had some value past 2011.
Again, it's easy to make these kind of decisions with the clarity of hindsight, but what's for certain now is that anything would have been better than what the Giants did, letting both players leave and without so much as an ounce of champagne showers. Anything would have been better than what the Giants did as now we are left with nothing more than a lesson to always consider the future.