I wasn't going to call the defense a glaring weakness, but you're right that it's not the same caliber as the Super Bowl teams. The WR corps is among the weakest in the league, at least among the contenders. Any team that considers Doug Gabriel as a possible #1 is in trouble. Now, they make up for that to a degree with one of the best QBs, a good running game and a couple good TEs, but if you can't see the WR corps as a glaring weakness, put down your homer blinders.
I don't think anyone in New England has called Doug Gabriel the #1 receiver. A lot of people from outside New England annointed him the #1 because they don't like the receivers there, but that's fantasy football at its finest. The New England offense seems fairly comparable to San Diego's offense last year. The starting receivers in New England will include some combination of Reche Caldwell, Chad Jackson and Troy Brown, who compare reasonably well to Caldwell, McCardell and Parker. Ben Watson leads the deepest tight end corps in a league that's trending towards using the TE more to exploit matchups; he's not as good as Gates, but the TE corps as a whole may be better and may produce more as a whole than Gates and co. did last year. Meanwhile the quarterback is arguably the best in the league, and while they don't have Tomlinson, the 2006 New England backfield seems fairly similar to the 2005 Chargers backfield. In fact, the New England defense has similar talent to that Chargers defense, with a couple young studs in the front seven and some questions in the secondary. Both have quality coaching staffs, although the Chargers coaching is deeper while Belichick is the better head coach. In fact, the biggest difference I can see between this year's New England team and last year's Chargers team is the schedule. New England appears to have an easier division, and plays the NFC North. If they can make the playoffs, New England has the better coaching staff and is obviously much more playoff tested. Overall, I'd say you have to consider them a legit contender right now.