Metroid is an exploration-based game. The game rewards you for finding secrets and for knowing how to get places. It teases you to find a way to break sequence, and much of the replay-ability of that game is based on the possibility to do that and to bask in what you've already learned about the world. Procedural generation takes a big dump on any sense of familiarity, which is a big part of the reward for exploration.
In fact, the _only_ games I've played where procedural generation were good for the game are story-building games, such as Rogue-likes and Dwarf Fortress. They reward you for building a story, not for traversing obstacles. In every other game, they are just a weak thematic obscuration of the underlying mechanical goals. The Dryad's name in Terraria doesn't matter. Dig deep enough and you'll find diamonds in Minecraft. Kill a boss enough times in Borderlands, and you'll get a good gun. There's no story about achieving these goals. Procedural generation doesn't participate in making the goals more interesting to achieve, it's a forgettable and incidental fact about something almost wholly unrelated.
Game developers need to stop trying to lean on it as a substitute for content. A game is what people can expect from it each time they play it, and if all it is is a bundle of mechanics and throw-backs, then there's not going to be much appeal.
