I havent played through one, and would be very interested to do so, but from the bajillions of clips around I think they have their own sound, and from those clips and the comparison clips with 'real' (i.e. valve) amps among the clips the sound is close, but no cigar.
For me to get one, the sound would have to work for me, and it doesnt. It clearly works for other people though, so I suppose you have to make that judgement for yourself.
What is clear and I think basically inarguable is whats already been said - if you need versatility or low volume high-quality-as-practicable recording, it pretty much cant be beat. I believe it can be rivalled with some of the better VST amp sims out there, including free ones, but for something in one box its looks quick and easy (compared to digging round and gathering VSTs) but expensive. The effects are also obviously excellent. A lot of the 'name' guitarists you see using them are using it for the effects with their favourite amps tones.
It does seem that the hype has died off. I think everyone was just surpised that the 'next step' in amp modelling was such a big one (and it was), but the novelty seems to have worn off: its not 'there' yet, from what I hear (and from what people like hunter that have had one have said; save that he doesnt like engls, he's usually got good taste ;)), and unless you need the versatility or lots of high quality effects, I wouldnt get it unless the sounds you hear really do it for you.