The difference is when I go to Melee tournaments, I always want to improve and I get like a zillion times better. Even since the last tournament, my play with Ganon has skyrocketed because I played those dittos with Goggles and now I know a lot more stuff that Ganon can do. (Plus I taught myself how to waveland consistently, which was kind of needed).
When I go to Brawl tournaments, after I leave I don't feel like picking up the game for another week, because there's just so much time you have to put into it in order to get good, and you have to constantly deal with Brawl's flaws.
When I say "more strategy" I mean with Brawl you have to space out your moves and play much more defensively-- in fact, the more defensive options you choose, clearly the better you'll be as you wait for your opponent to make a mistake (or just randomly trip, lawl). You can't string combos together with any reliability as any player with half a grain of common sense knows the right way to DI. In Brawl, you don't die from one big hit or a finishing combo, you die from fifteen little hits.
Brawl is just that much more of a cat-and-mouse type game, where you constantly shuffle back and forth, try to predict your opponents, and punish. The sad part about Brawl is even when you do THAT, you have to factor in the generally uphill climb of character balance. All the strategy and waiting in the world won't save you as you get caught in the ridiculous hitbox from a Snake Utilt and die at 80% or take 20 damage every time MK does a Mach Tornado... factor in the tech-chases, chain-throwing, projectile camping, planking, gimping and you generally have a much more frustrating, less accessible game.
Melee is just so much more compact, much more tech-skill based, much more offensive, fast-paced TACTICALLY oriented gameplay. The more experience with the game, the more tactics you pick up and learn, the more options you will have at your disposal-- that's what separates good players from bad in Melee. It's what leaves me with the feeling of wanting to improve and it's why I haven't stopped playing Melee.