I'd describe the texture as being a little sponge-like compared to, say, tinned tuna. The flavour is strong and slightly acid. The smell was pungent but not particularly awful.
On the whole I think people exaggerate; it's no more revolting than a strong cheese might be, and the "rotting herring" description you sometimes hear is about as indicative as "rotted milk" would be for cheeses.
On the other hand we had it outside and they do say it's much worse indoors. It was noticeable that the moment the tin was opened it attracted flies though!
Our host opened the noticeably swelling tin without a bucket of water, but he was an old hand at it.