I'll give my largely statistical take on the game. I can comment qualitatively on the Patriots having seen all their games, but I haven't seen any Chargers games this year, so I think a statistical comparison is the only fair one I can do. All analysis based on Football Outsiders stats, which are amongst the best:
FOOTBALL OUTSIDERS: Innovative Statistics, Intelligent Analysis | Methods To Our Madness
I think if the Pats play SD, it'll most likely be a close game, because the two best passing offenses are playing in the game against two mediocre pass defenses.
Breakdown looks to me like this:
Pats on Offense
Passing: Great Offense vs Mediocre Defense
Rushing: Good Offense vs Bad Defense
SD on Offense:
Passing: Great Offense vs Mediocre Defense
Rushing: Bad Offense vs Good Defense
Special Teams
Good Pats teams vs Mediocre SD teams
I'm using "Great" = top quartile, "Good" = 2nd quartile, "Mediocre" = 3rd quartile, "Bad" = bottom quartile.
Rivers, Jackson, Gates et al are the best pass offense in football this year and will move the ball and score on the Pats mediocre pass defense when they get their chances. But the terrible Chargers running game will not be able to keep the ball away from Brady if the Chargers get a lead. The Pats passing game is nearly as good as the Charger's, and Charger pass defense is equally mediocre, so the Pats will score on the Charger's as well. The Patriots *will* be able to run the ball on the Chargers, which might act to keep the score down as Rivers won't get many chances, particularly if the Patriots get a lead. Both teams have good turnover differentials, but obviously turnover luck could easily decide this game. Assuming no significant turnover edge for either team, it's very unlikely to be a blow out either way. A great Patriots outcome might look something like 28-17, assuming a big time-of-possession advantage to the Pats. A great Chargers victory might look like 35-24. Most likely is a relatively high scoring game decided on the last possession.
Caveats: the Chargers have been playing better lately than the full-season stats would indicate. The FO stats weighted for recent games still have the Pats the the better team, but it's now close, a 14% seasonal advantage reduced to 5% one weighted by recent games. The teams are a good match, especially given the Chargers will have home field, and the Patriots being an unproven road team. The biggest wildcard might be the Patriots defense, which has been the least consistent unit in football (32nd in variance) on a per play basis. Ironically the Patriots offense has been the most consistent per-play offense in football, but the defense is so variable that the Patriots rank 29th overall in variance. The Chargers have been a very consistent team overall (3rd in per-play variance), with the offense great and the defense good. The Pats defense could surprise either way, and will likely be the deciding factor in the game. Belichick will need to re-earn his defensive reputation. I would expect lots of novel scheming, but I'd also expect the Chargers to have figured it out by the 2nd half.