I'm currently playing through Super Mario Galaxy as Luigi. If you're not in the know, that means that I've already collected all 120 stars as Mario; in essence, I've seen the entire game. I'd like to comment on it.
Super Mario Galaxy is a perfect reflection of the soul of Nintendo. Its graphics, design, story, even title screen - everything in this game is emblematic of Nintendo's unique design philosophy.
The strongest impression upon finishing the game is Nintendo's dedication to quality. Perfection, really. Not perfection in the sense of creating a game that no one would have issues with, but rather, perfection in execution of the design. You might not like running and jumping around upside-down, but by God, you can't make running and jumping while upside-down work any better than it does in this game. Watching a "Secrets of Mario Galaxy" video on GameTrailers recently, I was surprised to see a glitch demonstrated. It feels that solid.
The game showcases amazing attention to detail. 1UPs aren't just scattered around the levels to liven them up; they are carefully placed to provide little mini-challenges. Luigi isn't just a model swap, he comes with his own sound effects and animations and even gets different reactions in conversation with other characters. That same GameTrailers video showed me one of Mario's moves that I wasn't even aware of - it's not necessary to beat the game, but just another little touch the designers put in. This game has been in development for over three years, and it shows.
In fact, sometimes I wonder if simply demanding that level of detail and quality is the real secret of Shigeru Miyamoto's success (Miyamoto is the creator of Mario and was producer of Super Mario Galaxy). In interviews it often comes up that he refuses to accept games that don't meet his standards. He'll scrap entire projects, months or even years into development. It's the type of decision that sounds obvious on paper but is gut-wrenchingly difficult in practice. Luckily, Miyamoto's got the stomach for it.
Super Mario Galaxy also showcases Nintendo's design philosophy: gameplay over everything else. That means gameplay over story, gameplay over setting, gameplay over graphics, even gameplay over innovation. Playing through Galaxy, it becomes obvious that Galaxy is set in space not because it tested well in focus tests, but because it allowed for abstract, fun gameplay within a cohesive context. Look back at the original Super Mario Bros. - there was nothing connecting the different worlds. As the series has progressed, it's taken on the trappings of story and setting which, while positive in some respects, have limited the variety and imagination of the series. Galaxy breaks free of any restraints by letting each world exist completely independently of what has come before.
The space setting also solves a problem designers have fought since the advent of the 3D third-person game: the camera. By setting the game on a series of planetoids, players never have to worry about the camera spazzing out when they run into a wall.
Miyamoto once said that an idea is something that solves multiple problems at once. Setting Galaxy in space was an idea.
Despite all this, there are still aspects of the game I would change. But as I said before it's not Nintendo's execution that I would change, but some of Miyamoto's design choices. Would my changes be improvements? To me they would, but I don't know if the mass market would see them that way. In essence, I don't know if a better game can be made.