A lot of my love for the game is nostalgia. We played so much Smash Bros in college it isn’t funny.
There are a number of factors that go into what makes the game great. Yes, it is a fighting game, but there are differences between this and your “typical” fighting games like Street Fighter. For starters, inputs are simple; you don’t need to remember your charge moves, circle moves, etc., you just press one of the two attack buttons with a direction. Further, instead of reducing your opponents’ life, you are increasing a meter with every hit. As your meter goes higher, you will fly further and further off the stage until you either can’t make it back, or are just smashed completely off the screen.
Stages aren’t your typical flat 2d stages, either. Each has its own layout with multiple ledges and areas. There is a lot of verticality to the game as well. There are items galore that assist you in battle and when some of the good ones show up, it can be a mad scramble or melee just to be the one to get the item.
So while the game is a fighter, it is as much a crazy party game that just about anyone can pick up and play. There is certainly skill involved, but it is a fun-for-all kind of game.
Plus, you can pick Kirby and drive your roommates into a blind rage just for picking Kirby…