I flew Biman a few years ago on the SIN-BKK route, on board their DC-10-30.
The flight attendants were very friendly and helpful. The flight wasn't full, in fact, there would have been about 50 people on board, and we were able to chin-wag with a couple of the flight attendants about cricket (which is getting bigger in Bangladesh by the way) for about half an hour.
The meals weren't world class, but one does not expect five-star meals on an airline which is in fact third-world.
The thing that really surprised me, is that they were able to serve me Aussie beer, Emu Export, which I found trippy, as I didn't think they knew about E.E. in Bangladesh.
The flight was uneventful and I would have no hesitation in flying them again.
From what I understand, Biman's domestic service has something to improve on, which I suppose is why GMG Airlines is doing well for itself (operates Dash 8s).