HI JUSTIN BAILEY!
(In a freak occurrence, the password Justin Bailey in Metroid actually worked. There is nothing that suggests that Justin Bailey was an intended code, it just worked by coincidence.)
You know what?
I hated Metroid and Metroid 2. Something about them just wasn't intuitive with the levels. You press start in Metroid and you get the ball and then you go into the strange crazy atmosphere that is Zebes, you don't know where you're supposed to go and the way the level is designed, it doesn't help you much either. Then you die and think, what happened?
It wasn't until Super Metroid that I really enjoyed the Metroid series, mostly because they both improved the level design AND they added the minimap. Now I wouldn't get lost so easily. Now I know where I'm going, what to do. It doesn't spell out everything for you, but the way the levels were designed, it almost guides you.
There are other things too (like how you can equip the wavebeam/icebeam instead of having to get it just to change what you had) but to me, those were the most useful changes.
If I fire up the original Metroid now, I still get mad, it's just really frustrating and I don't get it, I just get lost. The GBA remake they did was pretty cool, but I still get a bit lost because of the level design, it's just not as intuitive as Super Metroid. If I remember correctly, Metroid 2 was just a tad better with the level design, but... I still didn't really get it.
You know what else was cool about Super Metroid? The tutorials. There wasn't any. You just had an animal doing it and you had to figure out how you were supposed to copy it. Sometimes it sucked (it took me forever to learn how to wall jump, and I used to refused to go back down that passage until I had the Space Jump) and sometimes it was cool (learning how to store your hyperdash by crouching, and then doing an accelerated jump.)
I wasn't really interested in the Prime series though. I'm not too big a fan of FPS single player. And I think Team Ninja is doing the new Metroid or something and I'm still not really looking forward to it. Just give me back my awesome Super Metroid-type gameplay, please.