I can definitely see how some would be disappointed with the stage selection. For me, though:
- Yoshi's Island is the perfect Yoshi stage. It captures the look and feel of the SNES game perfectly, and I love how it cycles through the four seasons. I can't really complain about this one coming back as the Yoshi stage.
- Corneria, DK Jungle and Brinstar Depths are starting to feel a bit dated. They're solid stages, though. Corneria, especially, is an all-time classic.
- Green Hill Zone, Distant Planet, Wario Ware and Mushroomy Kingdom, being Brawl stages (like Yoshi's Island), don't really bother me much with their inclusion here. I'm actually looking forward to Distant Planet in stereo 3D.
- Flat Land 2 (it's the Brawl one, right?) is the perfect Game & Watch stage, much like Yoshi's Island is the perfect Yoshi stage. It offers so much variety and represents so much from the world of Game & Watch.
Is that all of the returning stages? Onto the new:
- Golden Plains looks a bit... plain, in Final Destination form, but the coin collection gimmick during normal play looks interesting.
- 3D Land looks AWESOME. So many platforms -- brick blocks, flippers, music notes, rising/falling pipes, tilting platforms, destructible platforms, rotating blocks, etc -- with left-to-right, into-the-screen and downhill sections. Just WOW.
- Rainbow Road looks really solid. Gorgeous and magical, living up to its name. I like that the spaceship and moonscape were included, since that was one of my favorite touches in the MK7 course that appears to be the main point of inspiration here.
- Paper Mario also looks solid, although there are so many great locations in the PM series that there was no way this level would approach its full potential.
- Gerudo Valley is a wonderful pick for a Zelda stage. So many nice touches: The familiar waterfall, river, rope bridge, carpenter's tent, and fortress over the hills... The Song of Time playing when the fallen bridge reforms... And the two witches casting fire and ice spells to shut down one-half of the level. Good stuff!
- Spirit Tracks is another wonderful pick for a Zelda stage. The attaching/detaching train cars, the platforms flown in from the sides and above, and just the sense of adventure with the background rushing by and the triumphant music playing... It makes me smile.
- Mute City is one of the coolest stages EVER. I mean, your mileage may vary, but the nostalgia for Mode 7 graphics hits me HARD. They're possibly the first videogame graphics I ever saw, when I tried F-Zero alongside Super Mario World at a friend's house. Seeing the battle play out across the tops of the vehicles and nearby platforms is something I never would've expected but that works so perfectly. Those vehicle sprites are GOAT; I love that they're now part of the battle!
- Magicant lives up to the legacy of Melee's Onett with the sheer amount of detail packed into it. Probably the most voluminous "fan service" stage yet. Flying Man, Buzz-Buzz's Grave, Brick Man/Dungeon Man, Sprout, Skyrunner... I think I even saw a Phase Distorter in there. And of course there are all the memories of Mother 1 and Mother 2. Coupled with the dreamy pastel hues and haunting music... Just a perfect stage.
- Prism Tower combines my love of traveling stages and stages that change from day to night and back again. Pokémon X/Y were easily my favorite installments in the series, so seeing and hearing Lumiose City brings back fond memories (even if that particular location was rather frustrating to navigate in the actual Pokémon games!).
- Unova Pokémon League grows on me every time I see it. Reshiram is one of my all-time favorite Pokémon, so I'm thrilled whenever he shows up. I haven't seen Zekrom in action yet, but I presume he appears there, as well. I do think the random appearances by Milotic and others is a bit odd, but ah well. The castle under a gathering storm is a dramatic backdrop. I like the bridges that slide in and out, as well.
- Reset Bomb Forest is a great Kid Icarus stage. Its Final Destination form has a nice atmosphere to it. And its normal form, with the stage transformation brought on by the appearance of Viridi, is memorable. Based on one of my favorite chapters from Kid Icarus Uprising.
- Arena Ferox looks solid. I always liked the Pokémon Stadium-style stages with the transforming layouts. I'm a huge fan of Awakening, and I suspect there are locations from that game that would've been more interesting, but I struggle to come up with examples, so I think this is a solid pick.
- Gaur Plain is another stage I really appreciate, especially now that I'm deep into Xenoblade Chronicles. Probably some of the best music on the SSB3DS soundtrack. I love seeing Mechonis in the background and the transition from day to night. Really interesting layout, as well, with two angled platforms on either side.
- The brief glimpses I've seen of Pictochat 2 look really clever, although I'm puzzled why it's not a Swapnote stage. Still, I have more nostalgia for Pictochat, so it's still a win.
- The Find Mii stage looks a bit simple, but I really like the look of the dark lord (or whatever you call the boss there). I'm eager to collect his trophy.
- Living Room is a stage I didn't think I'd like but that's really grown on me. I like the changing layout and the warm feel-good scenery. And that vocal remix of the bath theme is amazing!
- I haven't seen much of Tomodachi Life in its normal form. Its Final Destination form looks rather plain, but has a simple charm to it that reminds me of Pilotwings SNES for some reason (probably the blue sky and ocean). Catchy music!
- Boxing Ring seems a bit underwhelming on 3DS compared to WiiU, even if the layout appears to be similar. But I still look forward to playing here. I just wish there were more Punch-Out references in the form of appearances by other boxers.
- Tortimer Island is a GREAT stage. I love the changing layout and the fruit falling from the trees and how Kap'n appears there before quickly speeding off (sometimes with players still on his boat). The sharks are a nice touch. Great atmosphere in this level!
- Kirby's Dream Land is probably one of the freshest ideas for a Kirby stage I've ever seen (including all of the fan-suggested ideas). I would've preferred a full-color 3D stage was included, as well, but I definitely appreciate what they did here, and I like how the stage scrolls to a number of locations, and how your character is outlined when fighting behind the frame of the Game Boy's screen.
- Balloon Fight is a GREAT stage. It's based on my favorite NES game, and it hits all of the right notes. I really love the Final Destination form of this level, as well, which has the cliff elevated high above the pixelated waters. :-D
- Dr. Wily's Castle looks underwhelming compared to its WiiU counterpart -- an ominous castle doesn't work well in broad daylight -- and the stage suffers from the frequent appearance of the Yellow Devil. But there's still something appealing about the level.
- Pac-Maze looks a bit sparse after playing Pac-Man CE DX+ at length, but it still captures the ambiance of the arcade game, even in its Final Destination form, where a pulse of light radiates back and forth across the stage. Feels like you're in Tron!
I think that's everything, except Battlefield and Final Destination, but not much to be said about them.