As good as they are playing D, I'd still put them behind 99, 04 and 11. The level of offense we've faced hasn't been stellar. Good, but not great. Those other 3 teams shut down some impressive offenses.
With that said, this team is playing D at a very high level. I'd still describe them as special. Considering the personnel on this team, the level of defense is quite impressive. Props to KO and his staff and props for the players for buying in, learning and playing their hearts out.
I noted a whole bunch of times in the chat how high their level of intensity was. I guess as far as intensity is concerned, meaning playing with a lot of energy and sustaining it, I'd put it up there with the 2011 team. That team really stepped up the D with good but not great defensive talent.
2004 had some exceptional defensive players (Emeka, Taliek, and others) and the 1999 team had Ricky, KFree, Jake and some other very good defensive players, and I'd be remiss to not mention the 1990 team that had DePriest, Hennefeld, Williams, Burrell, Sellers and some other players who played the best 2-2-1 press I've ever seen.