As it looks likely that Barry is coming back, here's how I look at him at this point in his tenure:
Teaching, B-: It has taken too long to bear fruit, but I do think Barry is capable of communicating the scheme in a way that players can retain as evidenced by all the young/inexperienced guys functioning in the defense this season.
Culture/Buy-In, C-: Barry has had to weather the storm of some veterans who really don't care for their role in the defense, especially the better cornerbacks on the roster. Earlier this season when it seemed clear that he would be fired, there was minimal player-support in the media (though a little). That said, his defense never fully quit and obviously is playing hard now when it matters most.
Personnel Development, INC: Prior to this season, the defense was populated by lots of vets the Barry inherited that were past the developmental stage of their career. This season, there are a lot of young guys in the defense, many who are playing well, but it's too early to say how well they're being developed.
Personnel Deployment, D: Barry has failed to find ways to take advantage of what his players do best at a number of turns. Specifically, I think of how little they've used Walker as a blitzer this season, how Gary seems to be coached to rush high-side over and over to virtually no benefit, how Alexander and Douglas were so routinely ticked off.
Gameplanning, B+: I think this is Barry's best quality. He has demonstrated an ability to develop a good gameplan in big spots on a number of occasions (e.g. @DET, Vs CHI, this wildcard game, etc). No one bats 1.000 in this regard, but I think Barry is probably better than average.
Playcalling, D: The only reason this isn't an F is because they've become more aggressive and less predictable on defense since LaFleur took a more active role post-TB. Left to his own devices, Barry's play-calling is soft, timid, and extremely easy for opponents to pick apart.
Overall, C-: Barry isn't a disaster. He's competent in a lot of ways. But I don't think he adds value to the defense. I think what you put in is what you will get out. Lately, he's looked better than that, but we have seen that happen late in a season before and it hasn't carried over to the next year. Hopefully the improvements of this most recent surge will stick, but I'm not counting on it.