Yeah, it sounds like JH is out of action for the moment, which is a shame, but the whole place could do with a spring-clean, to be honest. We've (TSG) helped sort out the drainage problems at the bottom end, with all the water now captured and piped into Speedwell, but the top half is very loose, with water pouring in through the cartgate roof on wet days - one day one of those scaffolded chokes is going to start slipping...
As for the other deep ones, I think Rowter is fascinating, personally, and still to reveal more, I reckon. The miner's stairway at the very top end of the Upper Chamber is really special, and seems to lead to 'nowhere' - a place miners were not known for wasting their time on - the wall of stacked deads with no vein up there, and the boulder choke behind it has me puzzling.
Oxlow/Maskhill exchange is fab too - in fact I'm doing it in the morning! Needs a shedload of rope though - around 200m just to rig Maskhill. And trouble with Maskhill is the most interesting bits (from my point of view) are largely unreacheable from the rope! I'm going to try and have an explore tomorrow on the few horizontal parts, if time allows.