Finished today, definitely up there amongst the best Metroid games alongside Zero Mission and Super.
If they didn't have to make this a remake of Metroid II I'd argue it'd probably be the best 2D Metroid game of all time since the repetitivity of the bosses was forced by the original and Samus Returns does its best to add up to that to give more variety. I'm really looking forward to Metroid 5 since they even hinted at it in the photo gallery...