The initial reaction from nearly every analyst in the country is that the Royals GM screwed up royally here. Myers is already a great hitter, he has yet to play a big league game, so the Rays have control over him, and his very manageable salary, for several years, and if any other prospect that is included develops into a regular... then the Rays will be set on this deal. In essence the general consensus is that the Royals overpaid.
But lets stop and think about this for a second. The Royals are a small market team, that has trouble bringing in big time free agents due to the whole they never make the playoffs thing. Last year the Royals were 7th in the majors leagues in batting average, but 28th in quality starts. Last offseason they sent Melky Cabrera to the Giants for starting pitcher Jonathan Sanchez (who I believe ended the season in AAA because he pitched so poorly) because of their great need for pitching... needless to say they lost that deal. Sanchez was a streaky, realistically speaking, middle to bottom of the rotation starter, and they gave up a guy who started the all star game to get him. The Royals haven't developed a solid pitcher since well... a really long time by everyone's estimations. So by making this deal, the solidified their completely rebuilt rotation (other starters coming via Free Agency). And lets face it, the AL central is no AL east. Cleveland and Minnesota are down right pathetic, and those games should be now easy wins for K.C. The other two teams in the division are the White Sox, who some might say played above their heads all year last year, and fell apart down the stretch to miss the playoffs, and the Detroit Tigers... who are a legitimately good team that couldn't seem to put it all together until late even with the combined effort of a triple crown winner/MVP and former cy young winner... AND the Tigers don't have a bonafied closer going into the season (which is a scary measure for any team). One other thing to note, Prospect Wil Myers has proven through the minors to be strike out prone... while he is a GREAT hitter, when you get to the bigs, sometimes small problems (like striking out over 120 times in a minor league season) become big problems, because the guys up there are on a different level.
If K.C.'s GM thinks that adding a workhorse in Shields and a young talent in Davis (who struggled in Tampa, but AL central hitters will not be as potent) will put them in the playoff picture... then I say this deal isn't a huge loss for K.C. Yes, the Rays got a lot of talent out of this deal, Yes, the Royals may have overpaid to get these starters, BUT the Royals haven't got any great young arms in the wings, and if they aren't competitive soon, young bats like Hosmer and Butler may not stick around once free agency comes around. The inability to develop a good starter is the reason the Royals were forced to make this deal, but a playoff appearance makes this all worthwhile in my books. So in my opinion the Jury is still out in this deal, but I don't think this will turn out to be as bad as sending The Babe to the bronx or Lou Brock to St. Louis.