Metroid Fusion, originally known as Metroid 4, was in development for the GameBoy Color before being stopped and reworked for the GBA. In the gallery below you can see how different the Metroid Fusion beta was, especially in its early proto version shown in 2001. When the game was released in november 2002, the graphic was completely redone and many features were removed, as the ability to walk up on walls and ceilings.
Some screenshot from: http://www.classicgaming.com/mdb
Even the later beta had various differences.
This video showcases Metroid Fusion with an odd looking HUD, and at 0:07 you can see that the enemy’s right side is blown off, a feature not present in the full game. Other things are that title cards seem to have a different font, and at 0:24 there’s a scope icon at the top right. also, at 0:33 Samus seems to be wearing a dress.
In these videos there are some unused debug rooms, though the loading points WERE hacked to get them loaded.
In this one the X parasites look different, and at 0:18 the doors look completely different. Throughout the video the scope thing (as said earlier) at the top right has a wavy texture (Maybe radio or heartbeat monitor?). The enemies also respawn much faster than in the final.
There are also some unused music hidden in the final game’s code. You can listen them in the videos below.
Thanks to Mariosegafreak for the contribution! An archive of screens, info and videos of the early Metroid Fusion versions, can be found at Celebi23′s website!