There is obviously a good deal of thinking in Melee too, it isn't like it is super free, otherwise there would be no distinction between the good and the great. There is a LOT of thinking in Melee, but ONCE you get the hit, it is relative auto-pilot. In brawl, there are so few guaranteed follow-ups that you pretty much have to constantly be thinking, even as you are hitting your opponent. You have to think of what to do immediately after the hit to get the best stage positioning, as well as any potential reads that could allow you to get a 2nd hit depending on how they DI (if they DI away GL on getting a follow-up).
In melee, there are SO MANY MOVEMENT OPTIONS that it is really REALLY hard to get that first hit because you have to end up committing to SOMETHING, but a dash dance could lead to you getting punished, and the punishes are "ohgodwhy" in melee for a lot of characters. The extra movement options and the AMAZING flow of the game really make a huge difference in terms of high and top level play.
One thing that also sets Melee apart from Brawl, not in a good or bad way, is shield pressure. In Brawl you can pretty much punish anything you have on shield, which is why people just don't go in since they will get punished for free. In Melee, you hit somebody's shield with certain characters and you can just go off forever until it breaks, it pokes, or they try to roll in which case your STUPIDLY FAST CHARACTERS can just get to them and start a combo.
<3 Melee and Brawl, but PM is where it's at.