I went to the games Thursday and Friday. The lower 2 levels were pretty full for the sessions (which I believe are where the schools were all allotted tickets). The upper level - was not really at all. I think the listed attendance for our session was 12,000, which was fair (and also probably tickets sold vs. bodies...).
I was going to post my own "critique" of the tournament, but overall - I was not terribly impressed. It seemed a bit amateur-hour at times from a production standpoint (i.e. the "on court" host kept referring to Michigan State as Michigan in the game after ours which led to the MSU fans booing). You wouldn't really expect this from the "premiere" college sports conference (and richest). They had a bunch of Big Ten decals in the Metro station, but staged nothing outside of the Verizon Center - where an entire block was blocked off, but no "Big Ten presence" was there. If you're going to go into 'new' markets, at least make an effort. It's like they didn't even try to make it a cool event or have it be the Big Ten's first splash in the DC area where there are a ton of alums. It just felt like they checked off the to-do list and that was that.
One thing I will add as well - the Big Ten needs to do electronic tickets. This paper-only tickets for the all-session tickets, while I understand it's to make it harder to resell tickets - even though that's a complete reality of a tournament, it's also incredibly annoying in 2016 and probably hurts the overall atmosphere.