But having got to the right sonata at last: OMG.

Yes. There are places Haydn goes that no one else does. Before or since.

(Actually before turning to Schornsheim I subjected the Adagio to a test that few pieces survive. I bashed through it myself. If a piece can handle that it can handle anything.)

And indeed by the Ricercar Consort on a double CD that I have. I haven't listened to it for a while but I remember some absolutely hair-raising combinations of first horn reaching for the heights and second horn burbling in the depths, a little joke Haydn seems to have been quite fond of.

from piano sonata no.1 you hear (and see!) the jokes.
i love mozart, but you don't get that in mozart, do you?

I too go with popular opinion about Mozart and Haydn piano sonatas. Mozart fantasia (s) are good. Does anybody like them?

I've been puzzling away at this one. I don't know if I have any idea how I would explain Haydn to someone who didn't 'get' him. Perhaps either you're into the exquisite unfolding of forms and the play of familiarity and surprise or you're not? 

But no, a quick listen isn't going to do it. You have to give him time to build up your expectations to appreciate how he plays with them, I think; sometimes it's crassly, sometimes it's as subtly as any composer I know.

Now spinning here: slow movement of the 93rd symphony. Completely four-square for the first minute or so but so utterly exquisite it's put tears in my eyes. And then a huge Minore tutti just before the one-minute mark; and then back to the Largo cantabile as though nothing had happened. And then that oboe solo just climbing up the scale, and then... no, sorry, I'm just going to have to keep listening...

But does this problem arise often?  In various threads here people like me have come forward sheepishly and put their hands up to finding difficulty appreciating certain mainstream composers (for example, quite a few had problems with Brahms, myself included).  Does Haydn cause people similar problems?  I find there's almost always 2-3 Haydn disks amongst those on top of the cd-player in the "current listening" pile  

I am particularly enjoying this at the moment (and it's around a fiver on Amazon, too):

I wouldn't claim that I 'get' Haydn because I am always horribly conscious that there is far, far more there than I ever hear or am capable of appreciating but he is so central and endlessly rewarding as far as I am concerned that I was genuinely brought up short by the idea that people, whose views I respect greatly and who know infinitely more about music than I do, don't necessarily share that view. I can happily take it in my stride that people don't like other heroes like Berlioz or Bruckner or Britten or even Mozart  -  but Haydn! and the ground under my feet doesn't feel quite so solid any more. Gosh!

No moment of epiphany, though I do remember my heart pounding with excitement on hearing an earlyish symphony (thirtysomethingorother) conducted by Antal Dorati being broadcast from the Edinburgh Festival when I was also earlyish (ten or eleven). I just couldn't believe that the world had such things in it. And the quartets, above all, have been true, constant and faithful companions all my life.   

Sorry, generalised gushing doesn't help and is far more likely to be offputting   I'd just suggest almost any of the quartets from Op 55 onwards, say, and if that doesn't do it, well, it's a fair cop, I've been badly mistaken all these years.     

Quartet Op 76 No 6 now spinning (Quatuor Mosaiques)