I'm not really sure what to make of Brown. It certainly wasn't the highlight of his coaching career but there are a few things that make me hesitant to point the finger largely at him. For one, I'm not sure anyone this side of Pop has a better reputation as a coach than Stevens, so losing a head-to-head matchup with Stevens is not entirely an indictment of Brown as it has happened to a bunch of coaches. Not to mention Philly evicerated the Heat, which in and of itself is not entirely surprising since they have the much better roster. But if you consider Spoelstra is widely considered a really good coach as well, then it's a decent notch in Brown's belt.
Secondly, this is a team that is very much figuring things out. Now the Celts were really young too, so it's not a bulletproof excuse, but in the history of the NBA very few teams have gone from young and awful to young and title contenders in one season. It usually takes a bit of time.
Having said all that, Philly really struggled to execute in late game situations and clearly had the talent advantage, yet they only were able to win one game. If Brown is a really good coach, you'd have to figure it's at least a series that goes six or seven.
So yeah, there have to be questions.