A lot of fun on not enough space
So, as someone who grew up on Nintendo consoles and had played the 3 previous Smash Bros games avidly with his brothers, I was immediately drawn to Smash 4 when it was announced. I followed the hype and the videos for months before it came out, and the very night it came out, I downloaded it, my brothers downloaded it, and we texted our sister across the country to download it as well.
What I'm trying to say is, I love this series, and Smash 4 is an excellent entry, even though it isn't the Melee-destroyer that will probably never ever come.
Smash 4 is broken into 2 core experiences: Standard multiplayer Smash, and then everything else. Smash as a concept has remained pretty much the same over all the games: rack up damage on your opponents through combos, tricky plays, or just really strong hits in order to put them in a position where you can knock them off the stage or screen. Smash 4 takes the core concept and evolves it. It seems the developers tried very hard (like in Brawl) to make it accessible by reducing some of the advanced techs that Melee players used (or abused, depending on how you see it), but it also feels like they learned a lot from it: the entire game is considerably sped-up, characters are slightly more balanced, and there are fewer easily-exploited 0-to-death chains or combos that make the player on the receiving end feel like throwing their 3DS.
The biggest addition to the formula is customization: every Special move has its default mode and 2 more variants (that are randomly dropped in certain gamemodes) which opens up a ton of interesting "loadouts," and special parts which can adjust your character's attack, defense, and speed or adjust other effects, like spawning with an item, recovering when you get KOs, or dealing more damage when you're undamaged or over 100%. Most competitive players are stepping away from the special parts, as they are randomly generated and can be incredibly imbalanced in certain combinations, but the custom moves seem to be both an addition of choices and a potential way to balance a character (ban a strong Special move to hopefully bring their overall strength into line with other characters).
I'm not going to delve much into character balance or stages, other than to say that the characters feel very distinct, and the stages are gorgeous, even if most of them have too many hazards to be considered tournament-legal. They're still fun when you're dicking around with your friends or relatives, though.
The "other" section includes the usual single-player classic mode, all-star mode, stadium challenges (Home Run Contest, Multi-Man Melee, etc.) as well as the brand new Smash Run mode. It's a 4-player game mode reminiscent of Kirby Air Ride's City Trial mode where players run around a humongous map trying to nab whatever powerups they can in order to get an edge over each other in the minigame that follows afterward. It's really fun, even if there's minimal interaction between players on the map. The most you can do is find a switch to drop giant bombs on other players, likely KOing them and making them lose a ton of the stats they've picked up, essentially helping you maintain a lead or gain on the leader. It can only be played locally, but in a way, that's fine. It's best played with friends that you can shout at or slap when you see they're doing well, or acquaintances you can taunt after you've demolished them in the deciding contest.
Also included are an interesting selection of trophies (there are a lot, but not as many as, say, Brawl), a trophy-rush minigame, and more importantly, the Sound Test. You can play the sounds that nearly every character makes, whoopee, right? Well, more amazing is the ability to play through close to 100 songs on the 3DS from every franchise included in the character roster. There are recreations of the original soundtracks or modernized remixes, and all of them can be listened to even when the 3DS is closed, making it a Nintendo MP3 player. The sound quality may suffer from its compression, but being able to listen to music from Mario games, Zelda games, and even the amazing stuff from Xenoblade is just a sweet cherry on top of owning Smash 4.
Now, the game is incredibly fun. So much fun that it'll likely be played even after the Wii U version comes out. However, the game definitely suffers from its form. The 3DS is really not meant for Smash. There are a number of people who have already broken the circle pads on their devices, and I know my index finger hurts after playing for 3-4 hours because of the size of the 3DS (disclaimer: I have a regular 3DS, so it is possible that it's just the wrong size for me). The screen is small, so playing 4-player Smash can get really chaotic and difficult to track everything going on at once. Playing online is great when playing against people in your own state or so, but playing against players from overseas drags the game down into a lagfest where neither of you are happy. That said, I feel that it has its own niche. Playing against people you meet randomly during the day brings back that magic of finding someone else with a copy of Pokemon and a link cable, the spontaneous competition or camaraderie that can be acted on immediately. I'll probably continue to keep my 3DS in my bag for a long time to come just for the sake of challenging people out in the wild.
Overall, I'd recommend buying this if you're not so hardcore so as to require a Gamecube controller for perfect Smash playing, but still enjoy the fun that comes with every Smash game.