What I realized about the Smash Brothers franchise is that the additions they added didn't always enhance the gameplay...but actually hindered it somewhat.
Why I think the first is better goes back to how much fun my friends had with that game compared to the sequels. The first game was the go to multiplayer game if we weren't playing Perfect Dark. I liked Bomberman, but it didn't hold the appeal. The levels were simple, but worked. They didn't feel like there was too much movement or unfair traps...and overall enjoyable to play. The speed of the game was slower which allowed for players to take in the action easier. Let's face it all the smash brothers games could get chaotic, but the speed and simplicity of the first allowed it to be reasonable for all players, beginners and experts, which just made it more fun.
Melee comes out and really takes the formula and adds alot of depth to the game. Adding more throws, shield control, reversals, characters, items, everything just got bigger...but overall it felt like the same game. So why isn't this the go to game for Smash Brothers...for many it is. But for me, the speed and overall chaos of items and level design killed the experience. My friends still enjoyed playing the game, but often I found myself cursing the fighting system, and just played against people randomly hitting buttons winning. This game suffered from adding too much stuff without properly balancing and thinking about the changes and how it effects the players.
To me if Melee had better level design, item balance, and most importantly the speed of the original with some of the other enhancements it would have been better.
Finally, Brawl just continued the add more...but the chaos of Melee was already too much. Now stage hazards, even more items, assist trophies, pokemon, everything made the otherall experience worse...and its because the sum of all the additions made it worse than better.
Sometimes it is good to keep things simple. That doesn't mean you don't add new things, but you are careful with them. All 3 of the Smash games are still better than any other Smash clone game out there, the formula of King of the Hill gameplay just works for this type of game. So despite the complaints, I still feel the series is better than anything else outthere.