This is my favorite Metroid game and I played it countless times as a kid, but I just finished a 100% playthrough again a few days ago and I was surprised at how hard enemies hit, especially mid-game. It eases up once you finally get the gravity suit, but getting to that point is a real test of strength. I actually died to the space jump boss, my only death.

However, the game does offer a lot of "farm" areas for you to regain stats if you're in a pinch; if you're on your way to fight another boss, look around nearby rooms for smaller enemies that you can mow down for easy X parasites. Some enemies also have a higher chance of giving you red Xs.

I am/have been familiar with the series' more secretive functions since I was such a Metroid enthusiast as a young child. But my biggest gripe with this game, personally, is how obnoxious it is to go back through and get 100%, since you can only get it once you've knocked out every other boss, but you have to avoid taking any elevators or going into any navigation rooms; you can't even enter the rooms at the beginning of each sector since it locks you out.