Norrington here eschews any attempts to make points about period performance practice, and instead delivers a powerful but fairly "traditional" reading. He succeeds with what is most difficult--in movements like the Gloria, which can often be episodic, he maintains continuity and melds all the disparate episodes together into a seamless whole, while still maintaining the contrasts between them. Orchestra, chorus, and soloists are ideally balanced in the recording, and the soloists seem like a well-blended group, with none being too dominant or standing out by sounding different or worse than the others. Norrington's Gloria is exciting, and the rest of the work succeeds for the same reasons. Hard to believe this hasn't been reviewed yet, or received more attention than it has.
Listening again later (June 2015), I still find this to be an outstanding performance. The only slight drawback is in the recording--a slight bit of glare or forwardness when the full chorus is singing. But Beethoven's Missa is exceptionally difficult to capture on disc, and this minor drawback is no worse than you'll hear on most recordings of it. Still recommended.