Here's how I see it...
The skill is absolutely awesome and makes the game way more fun, even if it's not necessary to beat the game.
To teach the skill... it's tricky. I played Zero Mission before SM, and I figured out how to wall jump/shinespark there already, so it wasn't a problem for me. That's the thing with Metroid. Even when not trying to, you will accidentally wall jump here and there. That should be enough of an introduction. If the player is curious enough, he will explore this phenomenon and figure it out himself on his own time. That's how I learned it in Zero Mission. Forcing him into a pit like that is not ideal, imo, but it was the first time the devs introduced this feature, so you can't fault them for not knowing the best way to do this.
Compared to just a tutorial or text screen explaining it, it is way better, and fits with the atmosphere of the game very well. It's quite impressive in that sense. I still think the natural self-discovery of the technique is way better though, and I think the devs realized that with Zero Mission and Fusion.
The shinespark bird thing is kinda helpful tough, because unlike the wall jump, it's rare to accidentally shinespark... I know I never did it until I read about it online.
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_foolmo_
mobile computer