A few weeks ago, I had to opportunity to attend a Nintendo press event at SDCC where they showcased a number of upcoming games, including, for the first time, Metroid: Samus Returns. Unfortunately, it was the single game there that they didn't allow video or pictures of, so all I have to offer is my word of mouth.
The "demo" was essentially the full game, with reps cutting people off after the first acid level drop, so I was able to start a new file and begin a new game. The opening to the game was enough to tell me it was gonna be awesome, with a full on Wind Waker-esque slide show of exposition with awesome art to go along with it. The Nintendo rep was wondering why I spent so much time staring at the just that without even playing yet as I scoured it for new lore. Nothing that I can immediately recall threw up a red flag, and I continued through the landing sequence which seamlessly led into the beginning of the game.
One of the first things I noticed was how perfectly the 2D background parallax effect we're used to in the GBA games translated into 3D. At one point, the rep recommended I turn on the 3D slider to view it in 3D. I'm not one to use the 3D function often, but I figured he was doing his job, so I obliged. And man I have never been so happy to be wrong. Viewing the game in 3D make such a huge difference, it's likely that I'll personally play the entire game in it. The 3D background parallax effect I was already in love with turned into a world I was completely immersed in. On a side scroller. I'd highly recommend that anyone playing on a 3DS play it in 3D.
A few other little things I noticed: The beginning enemies are a little tougher than you'd expect first room/area enemies to be, which really helps you pick up and use the melee counter move more and more as soon as you learn it (I think in like the second or third room). FYI, the melee counter works beautifully as a natural inherent ability that it feels like Samus should have had all along. Wall jumping returns (in fact there was a missile expansion in the first area that I could only get if I knew how to wall jump), but it's the Fusion version, so no infinite wall jump, only back and forth in narrow-ish shafts. As I didn't get far enough to get Morph Ball Bombs, no verdict yet on if infinite bomb jumping is possible. The music was fantastic, the special blocks we're used to seeing in the GBA games translate wonderfully to 3D, and the door blocks that required a charge beam or missiles are very creative and natural.
The way that free aim worked was also a pleasant surprise. Much of the controls mirror the GBA controls, hold R to toggle missiles, and the melee counter is on the new X or Y button. You have use of the normal eight direction manual aiming by default, but when you hold down L (which in games past enabled the diagonal aiming), it turns her aim into free aim, using the circle pad to precisely control her direction. This came in handy a number of times, and the use of an already familiar button that I mentally associated with additional aiming controls made this another welcome addition to game and Metroid series as a whole.
One thing that did come off as a bit of a high learning curve was the use of the new Aeon abilities. You get one in the demo, which is a sort of localized scan pulse that reveals special blocks or otherwise hard to find things in the environment (hooray for no more Power Bomb spam), but the way to use it or switch to it had to be shown to me more than once. It utilizes in part the touch screen, which normally acts as a live start menu, showing a live full screen map, suit upgrades/options, and various menu options. This'll probably be something that I'll get used to the more I use it, but it's initial non-intuitive use was something that stalled me for a bit. That said, the ability itself was really cool.
The first Metroid fight went well, especially with the use of free aim and melee counter, which the game passively guided you in using a number of times before that point. I felt validation for being notorious bad at Metroid II Metroid fights. The hidden items were well hidden (it took me at least two full laps of the first area to get everything I could get at the time), and the overall flow of the first area was nice.
All in all, this felt like a near perfect translation of the 2D games I've come to know and love into being a 3D side scroller. I personally can't wait to stay up all night the night of release and play the crap out of this game. Hopefully my impressions have helped get you hype for it as well.
TL;DR, this game is a near perfect evolution of the 2D games and you should get it and you should be hype for it.