HD: Stallworth has talent to be sure. But that's not enough. As has been mentioned, he has attitude, injury, and substance abuse problems. There have been players with as many issues who have gotten big money deals in the recent past. Hell, Welker got almost 3 times as much guaranteed money as Stallworth, and the Pats traded picks away for him as well. So I wouldn't exactly call him a coveted FA WR, much less the top FA WR. Again the Pats taking-on a player like this is something that goes against what they've done in the past.
As for having a much better roster than last year, debatable at best. Thomas may or may not prove to be all he is advertised, but the track record of Ravens defenders after they leave Baltimore is pretty well-established, and Rosey Colvin hasn't come close to duplicating what he did with the Bears. And the trade-off of Dillon for Morris (a player similar to Faulk), Troy Brown for Welker, and Graham for no one isn't exactly scary. Add to that Vrabel, Bruschi, and Harrison aging rapidly...
Oh and the Pats were just as close, if not closer, to losing in the 2nd round (again) than they were to going to the SB (again). No more Marty to kick around, though and it looks like the Broncos are making serious moves to improve as well, and we all know how Shanahan has Belichick's number.