I enjoyed the first game simply because of the lol factor and the pacing was great and even if the game was unbalanced it was still fun. Never played Melee so I don't know if that was the happy medium of the 3, but from what I hear it may be.
Brawl....well it's probably the only time I have ever shared Yahtzee's opinion on a game. It was just a big pile of "meh", so underwhelming and just not fun.
The combat's pacing was just off and in conjunction with the combat mechanics themselves, fights just dragged on for far too long. It just takes way too long to kill people sometimes, and when you have many lives tacked on, the fight become a tedious grind.
Level design was hit or miss for the most part, and the controls felt disjointed and flat. The entire presentation of the game was far too busy, there was far too much eye candy and distractions that cluttered the screen. The camera didn't help alleviate that problem either.
Character balance I wasn't too fond of, but again that probably goes back to how much I disliked the control of the game. It was too button mashey for my liking too, and I never button mash in fighters. This one though had very little consequence to button mashing and hardly punished the player for doing so in my experience, unlike other fighting games where button mashing will only get you so far before the game penalizes you.
Bleh, you can see where I'm going with all this, I just did not like this game at all even with friends. The game didn't feel fun in the slightest and was just a big resounding "meh", and I was never hyped up about the game to begin with so I had no real expectations going in. I tried to like the game, but it was just so weak and too (oh god i thought I'd never say such an absurd thing) "casual" for me.
Anyways that's just my two cents on the game. Just wasn't the fighter for me.