When I was in one (1999-2000) it was a reasonably nice; semi-detached, 1950s or so construction but 1990s modernised, probably updated again since then. Garden was a bit poky but then we lived on the corner of The Oval so I got a sort of pie-wedge.
I was back there 2005-7 but living off base, although I didn't hear too many gripes about the quarters so I presume they were much the same.
The Officers' Mess at Henlow is nice, it's a bit older than the standard Lutyens '3 Arches' design. When I was there the presence of JACIG and the AME international courses gave it a nice degree of jointery whilst still being an RAF rather than tri-Service Mess.
One point to note about Henlow is that it is not that close to any large towns. Indeed, when I was first there all the quarters were regraded from A to B not because of any material problem with them but because the nearest major amenities (supermarket, bank etc) were about five miles away in Letchworth or Hitchin.