This battle is definitely my favourite from the Hoenn League, and possibly my favourite battle in the anime full stop.
I can see how Ash pulling something out of the bag when he's faced with a seemingly impossible situation at the end of a battle would appeal to people, but most of the time I see that, I can't help but think "There's no way he should have been able to get away with that". In this battle, the momentum shifted part-way through, which seemed realistic enough to get me more engaged. When Ash won, I actually felt like he deserved the win, which is a feeling I don't always get in his battles.
Katie had some good tactics going on there (something that I'd like to see more of in other battles), and the funny way Corphish dealt with confusion was just perfect to break through the intense tactical sparring. And the way it ended was superb - it made me think for a second that Ash had made a massive blunder, but I loved seeing him confidently give his final command, giving the battle that element of "trust" that the anime loves so much. That rounded off the battle well, satisfying me that it had it all - tactics, humour and heart.
My main objection to the two main battles in Hoenn that Ash had after this one is that they gradually deteriorated into "'Pokémon, use powerful attack X!' 'Pokémon, meet it head-on with your strongest attack Y!'", but this had none of that. Good job, writers!