I've only just seen your message. I went to Margate in August mainly to see the gallery. Rather like you I was disappointed by it's emptiness, unlike the excellent new Hepworth Wakefield I visited later in the month. I don't think I really expected to see many Turners though.
The building from the inside was good - especially the view out of the big window and the reflections of reflections. However, like many modern galleries it was a case of design over content. I struggled with the small font, dim lights and signage. It took me ages to work out which door led to the loo. I didn't find the staff that helpful either. The cafe was nice but expensive - I did treat myself to a really lovely knickerbocker glory. Not so sure about the exterior view but having read the reasons for the design I can begin to understand it.
People in the town I spoke to about it's role in regenerating Margate said it is making a difference which I'm pleased about but I think both Margate & Fokestone ( I went to the Triennial too) have an awful long way to go.