So I just beat this.
52%
9:14
As you can see, I didn't try to explore much or go out of order. That's just not the done thing the first time through a Metroid. It certainly felt more open than Fusion did.
Although I don't think it was nearly as offensive as people were worried about, it is true that the cutscenes just kept getting dumber and dumber. There's just no two ways around that. However, when the core gameplay is as good as it is in this game, I'm willing to overlook a lot of bad; a lot more, it turns out, than I actually had to.
The only time the gameplay really got on my nerves was the final boss (before the credits), because it consisted entirely of a gimmick. However, the penultimate boss ([spoiler]a Metroid Queen[/spoiler]) was five kinds of awesome, and [spoiler]the extra boss after the credits (Phantoon)[/spoiler] was at least eight kinds.
Significantly, this is the first 3D game I've ever played that felt 2D. It took until 2010 to make that happen, but they did, and it is great. I hope this point doesn't get overlooked when it comes time to do the retrospectives.