For me, the highlights were The Darvaza crater and generally being out in the Turkmen desert, along with the archaeological sites at Gonur Depe and Merv. Also, the three castle climbs in north-eastern Iran and the scenery around that area.
In regards to accommodation - brilliant overall. In fact several of the hotels were of a standard above what I would expect on an adventure tour. Food was fine and plentiful…and such a relief not to have to split the bill with other travellers after each meal!