I thought it might be interesting to go year-by-year through the units Knapp has worked on, looking at DVOA for quarterbacks and the offense as a whole, with the years before he arrived and after he left as a point of comparison.
San Francisco (1998-2003)
Year Position Offense DVOA QB QB DVOA
1997 N/A 2.3% (10th) Young 28.1% (2nd)
1998 QB coach 25.1% (2nd) Young 25.9% (8th)
1999 QB coach -7.3& (16th) Garcia -2.8% (24th)
2000 QB coach 17.8% (5th) Garcia 29.4% (3rd)
2001 OC 18.5% (1st) Garcia 13.9% (4th)
2002 OC 21.3% (3rd) Garcia 15.9% (9th)
2003 OC 5.9% (11th) Garcia 2.2% (15th)
2004 N/A -20.2% (29th) Rattay -16.6% (30th)
Tough to give Knapp too much credit for the rebound of the 49ers offense as a whole in 1998, given that Young's level of play remained essentially unchanged. However, I do think that getting roughly league-average play out of Jeff Garcia in his first NFL season (having not taken the bulk of the reps in pre-season, since Young entered that season as the starter), and then elite play in his second, reflects very well on Knapp's performance as a QB coach. As offensive co-ordinator, Knapp oversaw two seasons of dominant play in the system he had been brought up in (and which is closely related to the one he will be working in with the Texans). Mariucci was then replaced as head coach with Dennis Erickson, who implemented a half-assed cross between the existing West Coast offense and his own, more deep ball heavy system, which was probably a bad offense in the first place and certainly didn't suit the personnel (especially Garcia). Factor in the injury problems the team had to deal with that season, and I'd actually see getting above average results as an excellent outcome for Knapp. He then left, as did Garcia, precipitating an absolute collapse from the 49ers offense which probably tells us rather more about Erickson than Knapp. Overall, it's hard to see Knapp's 6 years in San Francisco as representing anything other than excellent performance, albeit in favourable circumstances from a talent point of view.
Atlanta (2004-2006)
Year Position Offense DVOA QB QB DVOA
2003 N/A -11.1% (24th) Johnson -11.1% (29th)
2004 OC -9.4% (24th) Vick -31.4% (37th)
2005 OC 2.5% (12th) Vick -10.7% (29th)
2006 OC 0.0% (16th) Vick -20.1% (38th)
2007 N/A -15.5% (27th) Harrington -5.8% (29th)
The "before and after" years aren't actually much help here in providing context, as Vick saw significant time in neither of them, whereas he played almost every game in Knapp's tenure. Knapp took over a bad offense which was still bad in his first year before improving to average in his second and third. As in San Francisco, he then got the boot as the team brought in a monumentally incompetent college coach to oversee a total clusterm'kay. Subjectively, I always felt that it was a mistake to try to shoehorn Vick into a West Coast offense to which he was manifestly unsuited, and a fair part of the blame for that has to fall on Knapp (though they did experiment with some college option stuff in 2006, which worked ok but not great). Fundamentally, though, I think Vick was always going to be a coach killer, and it's not as if Knapp's Atlanta units were anything resembling a disaster. Overall, I'd consider his time in Atlanta a slight negative, particularly with regards to his flexibility.
Oakland (2007-2008)
Year Position Offense DVOA QB QB DVOA
2006 N/A -36.5% (32nd) Walter -45.6% (46th)
2007 OC -17.4% (28th) Culpepper -4.9% (27th)
2008 OC -21.3% (31st) Russell -16.0% (34th)
2009 N/A -22.4% (30th) Russell -57.2% (45th)
Honestly, I'm not sure anyone can conclude much of anything from anything that happens in Oakland. That franchise will continue to be a catastrophe as long as Crazy Al the Lich King is in charge. In Knapp's first year, the offense took a big step forward from "inhumanly awful" to "really bad", but that could well be simply because even semi-washed up post-injury Culpepper is a huge improvement over Andrew Walter. If you thought Jamarcus Russell was a good prospect, maybe you blame Knapp somewhat for not developing him. Personally, I thought he was highly likely to be a colossal bust before he was drafted, and certain to be so once his ticket was punched for the Black Hole of Suck. It may or may not be noteworthy that under Knapp in 2008, Russell was merely pretty bad, where in 2009 he was historically awful - another season like that and he may pass Ryan Leaf to claim the title "Biggest Bust of All Time" (and I'm not talking man-boobs). Neither Culpepper nor Russell was a good fit for a West Coast offense, most of the rest of the offensive personnel (especially the receivers) were terrible - I just don't think there's much of interest to be drawn from this phase of Knapp's career.
Seattle (2009)
Year Position Offense DVOA QB QB DVOA
2008 N/A -9.7% (26th) Wallace 7.3% (19th)
2009 OC -17.9% (29th) Hasselbeck -21.1% (34th)
The Seahawks may not be permanent no-hopers, but they certainly are in a rebuilding phase. As bad as a banged-up Hasselbeck was in 2009, he was considerably worse in the half-season he played in 2008. The once-vaunted offensive line has crumbled: Walter Jones in particular is a shell of his former self. John Carlson is a fine tight end, but the receiving and running back groups are pitiful. This unit was bad because the talent was terrible - I don't think scheme or coaching really had much to do with it.
Conclusions
When given good personnel who fit his system, Knapp has run excellent offenses. He also appears to have done a very good job developing Jeff Garcia. He has produced improvement over the previous season in his first year in three out of four stints as offensive co-ordinator. However, there is a suspicion that he is unwilling to adapt his system to suit his team's talent, and he is not so brilliant an offensive mind as to be able to get good or even solid performances out of truly talent-starved units. However, he is coming to a team that runs a system very similar to his own, with offensive talent that resembles the 2001-2002 49ers far more closely than it does the 2004-2006 Falcons, never mind the 2007-2008 Raiders or the 2009 Seahawks. I believe Knapp probably deserves another shot as an offensive co-ordinator in the NFL, on a team with players suited to the system, and as such I am very happy to have him on board, be it as a pure QB coach or a de facto passing game co-ordinator. I'm with you on this: hard to see how the coaching hires this off-season could have gone much better.