Even though Metroid: Samus Returns is a remake on a Game Boy Original Title, there have been a number of updates made to the game. The storyline may remain the same as before, but many new features and mechanics have been upgraded, especially where Samus' Weaponry is concerned. For instance, in the original, Missiles were the only known Weapon that was effective against Metriods. But now, Samus' Ice Beam works on them too.
Another necessary change has also come to the Weapon upgrade system. In the original, upgrading a weapon meant losing your previous upgrade. You also had to find a Chozo Statue with the weapon you wanted if you ever wanted to return to a different weapon. This made the original quite a hassle at times, but that is no longer the case in this remake. Now, whenever you'd like to get or switch to a new beam, your upgrade will actually combined with the previous one! This means you can switch back to certain beams and missile system at any time!
Another drastic change comes where th map is concerned. While the general layout of areas and rooms remain the same, almost all locations have been redesigned. Some areas don't even slightly resemble what they did in the Game Boy Original! A number of extra rooms have also been added, some have even been combined, making the overall layout different in some cases.