Ho!  I confess that I find Cosi and Idomeneo rather overlong.  Figaro is, for me, perfect.  The widely ranging, clever plot is permanently satisfying with the many discoveries in its byways that you only find after many performances.  I think that musically and dramatically it is a perfect theatrical work and I would class it in the top half dozen of all operas.  For some reason, and the fault is probably mine, I can't stand the Don.
Cheers

Unfortunately Bohm's response to Cosi's length was often to make swingeing cuts - particularly evident in his 1974 live recording from Salzburg (which in many other respects is a really fine performance), but in his earlier Decca recording too.  I'm not sure that playing around with the structure really helps.

As many above have noted, it really does depend on the performance. I always thought La Clemenza di Tito a dreary and overlong work. But I saw a fantastic performance recently at ENO with Paul Nillon, Emma Bell and Alice Coote that really changed my mind on this piece. It can work the other way too. I think Verdi's Luisa Miller is a superb work. However, I made the mistake of going to a dreadful concert performance at the EIF a few years ago. Granted that concert performances can be difficult, but this was awful, with provincial singing and a conductor who clearly had little or no understanding of the idiom or affection for the piece. Just goes to show that there are no 'indestructable' operas 

Yes, that's the one, I could only offer a vague guess at the year I'm afraid.

The clarity of the ensemble is still very clear in my memory, the performance seemed so nimble yet full of gravitas. That was the only time I ever saw Bohm and he had an almost god-like presence it seemed. (And thanks for the reminder of Hermann Prey's wide-boy behaviour  )

...whereas I see that Glyndebourne produced it, conducted by Fritz Busch, in its first ever season in 1934!

With regard to the length of Mozart's operas, Reiner, I think an awful lot depends on how quickly the performers pass on the baton - applause after every musical number can do terrible things to the length (and SEEMING length) of a performance, and letting the recit sag is just as bad. For Zauberflote and Entfuhrung, it's equally important to snap the dialogue back and forth, no long pauses unless they're wanted for dramatic effect (e.g. Tamino's trial of silence). The size of the theatre is a contributory factor, it's much harder to keep the thread taut in a large house like the ROH or the Coli than in a smaller one like Glyndebourne or the Leeds Grand. I saw a Cosi at the Coli not too long ago, where the conductor (sorry, can't remember who) was razor-sharp in picking up the recit as soon as the preceding aria had finished, crashing through applause where necessary. It kept up the tension and shortened the performing time dramatically, whereas at the latest ROH series the otherwise immaculate Colin Davis allowed applause after every number, and the whole thing felt so slow, too slow.

The cut bits... It's worth bearing in mind that all the Da Ponte operas are habitually performed with cuts nowadays. Ferrando usually loses "Ah, lo veggio" unless the tenor has a cast iron constitution, the boys likewise lose their Act 1 duet, and the recits before the Act 1 finale and "Fra gli amplessii" get trimmed. In Don Giovanni, the Leporello/Zerlina duet nearly always goes (the late lamented Opera Factory performed it some years ago), along with Masetto's recit which ties into Giovanni's subsequent account of his adventures. And of course in Nozze, Marcellina and Basilio often lose their arias. Usually I think the cuts are a good idea, especially the Figaro arias which hold up the action just when we need to motor on, although when we get a really good Basilio I sometimes wish he could have the aria (like the sublime Alan Oke at the Coli earlier this year, and I would like to hear John Graham-Hall do it once - I remember Ryland Davies bringing the house down with it for WNO some years ago).

Ottavio... An interesting article in the Glyndebourne programme some years ago suggested that Ottavio has something in common with Yeletsky. Both gallantly stand aside to give their troubled ladies some space and let them sort themselves out, when what the ladies really need is someone who'll sweep them off thier feet and take charge. It's too late for Yeletsky at the end of the opera, but maybe - depending on the interpretation - Ottavio will get enough courage to tell Anna to stop shillyshallying. I've seen Ottavio played as everything from dumbcluck (that awful production from Belgium at the Coli which preceded the even worse Bieto one) to grave, ageing senatorial type (the Peter Hall production at Glyndebourne). I think it's important that he is given dignity and substance as a counterweight to Giovanni. He's actually more forward-looking in some ways: Giovanni uses a sword, Ottavio the more modern pistol. Ottavio's the one who eventually decides to call in the authorities, though whether he'd have a case which would stand up in court is a matter for conjecture (he might have stood a better chance if Leporello hadn't just escaped). We don't need him to be comic relief, Leporello's already doing that.

I've said it before, but I don't think Mozart was a natural operatic composer.

In order to create successful operas, you need to have an understanding, and appreciation of, drama.  And drama is what WMA's operas tend to signally lack.

I find 'Figaro' painful to listen to...an endless A stream of 'nice' melodies, stretching on into infinity.  Fine for about an hour (at most), but then I get fidgety.  The last Covent Garden production was a real ordeal to stand through, I found....

And I'm afraid I find his opera seria terminally dry....though I'll grant you that Idomeneo finally catches fire when Neptune's statue makes its contribution. 

As for the Flute.....I always tend to drop off after the initial scene-setting.  Though it does contain some fine music.

DG has a great conclusion (I do like the 'vice punished' bit at the end), some lovely individual arias and not much else.  It's no flawless masterpiece and it would be foolish to claim it as such.