Kotaku says that the majority of the cutscenes and supporting cast are at the beginning and end of the game.
Anyway, it doesn't look like I need to finish the Prime Trilogy before jumping into this game, so I will probably play it on Tuesday.
EDIT: Okay, so I read the Destructoid review. Here's a recap (my thoughts are in parentheses):
-story is "absorbing and at times even moving"
-"these are high quality cut-scenes, with superb direction and visual flair", but some last over 10 minutes
-auto-aim replaces manual lock-on, no way to strafe
-combat is akin to "run away to charge, then turn and fire", evasion works well (has combat in Metroid ever been different from "enter room, start shooting"?)
-"when battling one-on-one with a beast of monstrous proportions, you’ll generally run into fewer targeting and Wii Remote issues" (in Prime I rarely had to do a lot of strafing and targeting outside of boss battles)
-finding hidden stuff: "it’s not quite exploration as much as it is “poking around a room to find a ledge or hole.”" (pray tell what the definition of exploration is then: Prime had everything mapped out too, it's just a matter of getting there)
-unlocking items: "the game basically holds your hand and screams “It’s time to use this!” in your face." (have you never played Zelda? The new item you get is the item you need against the next enemy)
-graphics: cutscenes are great, women are awesome, men look like meatheads, some questionable enemy design (sounds to me like it's objectively great)
6.5 seems kind of low. It may not be the "high standard" that Nintendo produces, but even Nintendo's worst is still better than most others. I think the reviewer was more disappointed that it wasn't "classic Metroid".