Just finished this game. It's a neat experience, but this won't surpass a true modern Nintendo-developed experience. If you compare it to Metroid Zero Mission, for instance, it loses badly.
My biggest gripe with this is that the level design can get pretty boring to incredibly uninspired very fast sometimes. In the end the game became so incredibly "un-hype" that, when I reached the final boss I was like "No... No man, there must be something else." I understand perfectly this is a remake, but it doesn't mean they shouldn't have improved where the original lacked.
Long stretches without a single enemy or plaforming challenge are common from halfway on the game onwards, and the further you progress, the lazier the level design becomes, almost as if the dev became too eager to see it finished nearing the end. Secrets, also, are very few (some of which are really smart, but most being ordinary).
The Spider Ball is criminally underused. When you acquire the Spring Ball, the Spider Ball becomes more like a nuisance than an upgrade.
The pros are the bosses and the Metroids. I loved how original the dev got with some ideas. The graphics are ripped from other Metroid games, but the new graphics are interesting and well done.
If I could rate it, this game would be a 6/10.