Depends. Kingdom Hearts 1 had a bit more strategy to their gameplay mechanics. It was worth using everything at your disposal. Kingdom Hearts 2 kinda killed summons, maybe even magic (I can't recall). I found the story more heart felt in 2.
iuno - the summons were pretty whack in both games to the point I barely used any except for testing purposes to see how they were lol. Magic wise - you can survive the entire game for both games without much magic use (offensively speaking) - the only main magic I've used for both games were Cure along side Aero (the shield spell). KH1 although required you use certain spells to open up passages (in the traverse town districts) and to attack those mushroom heartless to gain specific items to create accessories and stuff.
But ya, KH2's gameplay expanded due to the forms, Quick action events, and with the addition of a huge arsenal of skills/techniques the player could use depending on what they have equipped, etc.
I also found the accessory system to be more worthwhile in KH1 as it was more beneficial than KH2 where it felt like it was something that was super minor.