If you enjoy turning over the bones of the beautiful dead while sobbing piteously, check out these design documents for a rejected "Metroid 1.5" proposal from Retro Studios.
A vast posting on Neogaf revealed the documents, apparently snaffled from the website of Retro level designer Tony C. Giovanni.
As well as a stockpile of breathtaking concept sketches, the documents mention an intriguing multiplayer mode, allowing a second player to control a "mecha" or "shadow" Samus.
Apparently focussed on puzzle solving and ball-mode navigation, the game would be set on a ship the same size as Metroid Prime's ruins and mines put together.
The plot concerns a rogue navigational AI, so intent on foiling Samus's attempts to escape that it disrupts gravity, time and causes further "environmental weirdness".
The information is mirrored on the Metroid Wikia, along with various explanations of how the lost title would have fit into the series' canon; it's well worth a weep over if you're a fan.