Like the Nintendo Media Summit presentation, the E3 demo started at the beginning of the game. After a thrilling cutscene recapping Samus's defeat of Mother Brain at the end of Super Metroid, and the tutorial sequence, the scene cut to Samus investigating the space station "Bottle Ship." Here she met up with Galactic Federation officers, including Adam Malkovich, who bears a grudge against her for leaving. Courtesy toward Adam and the military is the frame for Samus's inability to use her weapons -- she refuses to use missiles or bombs until Adam "authorizes" them. This means, of course, that the Galactic Federation soldiers aren't just useless, they actually hamper Samus's progress.
As previously noted, the level shown at E3 was not a new one, so I won't belabor the description. It involved shooting swarms of enemies in both side-scrolling and first-person modes, some light puzzling, and a satisfyingly tall triangle jumping sequence. At the end of the demo, the Galactic Federation jerks proved themselves useful by freezing parts of the miniboss so I could fire missiles at it, after dodging its attacks.
I was impressed by the versatility of the game's perspective-switching. You can use first-person pointing (with the Wiimote) for precise aiming at bosses or fast-moving enemies; you can (and must) use it to scan items in the environment, in order to activate elevators and solve other puzzles; and you can use it to target and fire missiles.
I was also impressed by how possible it is to choose not to use it outside of scanning or missile circumstances. At first, I had a hard time getting the Wiimote to recognize my movement when I pointed it at the screen -- either because I was moving too quickly or lights from the show floor interfered with its functionality. In any case, I eventually got it to work reliably, but as a result of my early failures I was hesitant to use first-person mode.
For most of the non-boss combat sequences, the third-person perspective served me just fine! There were areas where the screen filled up with small, quick enemies, and I could tell the game expected me to go into first-person, but I decided to run, jump, and shoot instead. It's a trade--off: you can use more weapons and have better control of your aim in the first-person mode, but you are rooted in place.
In fact, I suspect that's why Samus is so much faster in this game: to create balance between the third-person and first-person segments. The disparity between the hyper-speed running and the immobile first-person mode created tension which, in turn, made the game exciting. I grew more comfortable with the mechanic of switching into first-person mode by the boss battle, as well, so I expect I'll experiment with it more when I get a chance to play the final game.