Matt... OUTSTANDING review of Metroid!
You pretty much nailed all of it. And you didn't do so bad at the gameplay either. You're quite right about the difficulty here... Kraid, the first boss, requires a butt-load of stuff to beat. The game is much, much harder than the later games in the series.
Heck, just jumping from Metroid to Metroid II - The Return of Samus, is pretty dramatic. You gain so many more weapons and abilities in the later parts, that give you an unbeatable EDGE against the enemies. Now, I've speed-run every single one of the later games, and gotten all of the good endings, I'm quite the fan, I guess I could say. But I've never beaten the original one... Even tho I've got it for the GBA ( it's an extra in the remake, Zero Mission), so there really is a big, big difference between the first game and the ones that came afterwards.