I'm really impressed with the game so far. At first the only thing I didn't like was that it was bouncing me around to the different biomes without letting me go back through and explore them all, but I hit the point in the game where it opens up more now, and I think it was mostly a good decision. It took me a while to figure out where the hell I was supposed to go after getting the speed boost. Got quite a few tanks and missile upgrades along the way though, so it's no big deal.
The controls are surprisingly intuitive for everything for me so far except the grappling beam. My hands just go full on stupid when I have to do a jump into using it since you have to hold so many buttons at once to aim it.
Bosses have been great, love that there's always a bonus bit you get for doing the fight well. My reaction for the Kraid boss was a little off so I didn't get to see the cool cinematic if you manage to get the melee counter to hit.
Mercurysteam really delivered here. If I had one complaint, it'd be the music has been mostly meh so far. Still, every now and again when that Super Metroid theme hits, it's pretty sweet though.