As hard as this plot was to swallow (as soon as I heard "the earth shall turn to ash" I immediately put two and two together and thought "Oh, my God, that's ridiculous"), I still remember liking it a lot upon its initial release. I remember it well - it was during the week of my annual family camping trip, and my dad drove me, my sister, my friend, and my sister's friend out to the theater. Of course, my sister and her friend went to "Nutty Professor II: The Klumps", so my dad took me and my friend to this. Despite a brief, screen-darkening technical difficulty halfway through the film (I still don't know what happened), I remember having a good time, especially exchanging little asides with my friend at certain scenes - when Misty says "You act like Pokémon are just things to collect like cards or toys!", I turned to him and whispered "Absurd, isn't it?" I also vividly remember staying behind in the theater to listen to the ending credits music - and booking it towards the exit at top speed when I heard "Polkamon" by Weird Al Yankovic. No offense to the guy, but the song didn't belong on the credits.
I think Jessie, James, and Meowth totally stole this movie for me. Though usually I despise it when they temporarily go good, I forgave them this time because otherwise it would have meant world destruction. And they got a lot of good lines (I'm surprised their "opposite sex" routine was even in the movie), plus their ending discussion with James going "That's good! That's bad. That's good...or is that bad?" made me laugh - even moreso when I found out that they lifted it from an episode of "The Simpsons".
Only downside to this movie - the promo cards. All the theater had was Moltres, so I wound up with three of the same card (my dad didn't want his, and my friend gave me his). At least they made good trading collateral later on - I think one of them was involved in the four-card trade that got me my unlimited Base set Charizard.
On a final note, Slowking's "I could use pants" is one of those rare times when 4Kids' dub alterations actually works (and I still don't know why they cut Tracey's explanation of the chemical reaction between Articuno, Zapdos, and Moltres' attacks).