I love Super Metroid's.
It's easy, but not too easy. It feels good to get a grasp of it; at first it feels like it will be very difficult. It doesn't feel forced upon you either. Games like NSMB or Mega Man X kinda throw it at you, can make it hard not to stick to walls when you don't want to; that style feels like it slows the pace a bit.
It's flexible. You can go up a single wall, you can change up the timing. It feels useful in plenty of spots to smooth out traversal, and lets you feel like your character is more agile. It gives the game a stronger sense of control, and makes much of the environment feel more interactive.
There's a visual indicator. The little pose Samus does just before you wall jump adds a little discoverability and just makes it feel cooler. WJing off of enemies even adds a small touch.
They teach it to you. SM's two 'advanced technique' tutorials are wonderfully handled: a little out of the way, and they aren't too heavy handed. You won't be stopped and forced to read through instructions, you'll just see and then hopefully do.
You rarely ever need it, but are able to use it often. The way it works, the way the game is built, give you this sense of being able to do something outside the normal limits of the game. Of course, really it's a basic feature and the level designers have it in mind. But the way they let you do things with it is wonderful; they don't try too hard to lock you out of every possible situation where the wall jump would be useful.
Imo it adds a nice extra layer to the controls of the game and is a very welcome mechanic.