Moorland accommodation failed to impress (4,4)
I believe the answer is:
fell flat
'failed to impress' is the definition.
(to fall flat is to fail or go badly)
'moorland accommodation' is the wordplay.
'moorland' becomes 'fell' (fell can mean a moor).
'accommodation' becomes 'flat' (I've seen this before).
'fell'+'flat'='FELL FLAT'
(Other definitions for fell flat that I've seen before include "failed to impress" , "collapsed" , "provoked no interest" .)