For the most part, not much has changed about the Kirby series — many of its titles are fairly straightforward platformers in which your main ability is to suck up enemies and acquire their powers. It's not until somewhat recently that the development teams started trying different things, and one can certainly make a case saying that Kirby & The Amazing Mirror was one of the first games to truly do so.
At its core, this is still quite similar to a traditional Kirby game. The pink fluffball still has the power to steal enemies' moves, after which he can use them against their original owners, and he has his usual move set that includes slide attacks, the power of flight and more. However, the rest of the game is a bit different from its predecessors — this time, you don't go through relatively short levels one by one, rather, you explore one giant, interconnected world divided into several areas, not unlike a certain other Nintendo series which features a female bounty hunter.
The game's many areas are not simply a collection of small, easy rooms you can quickly run through — each of them features several puzzles, alternate paths and secrets to discover; there are many times where you will need a particular ability to progress, which can lead to frequent backtracking. Each area also has several mini-bosses, but you'll have to find and defeat the main boss in each area to truly clear it and get one step closer to unlocking the grand finale.
Unfortunately, this doesn't work as well as you might imagine. Although there is a hub world which is connected to many of the other areas, it's not actually connected to all of them — you'll have to take unnecessarily long, confusing paths through other areas when it could've been as simple as having a locked door in the hub open upon defeating a boss.
Backtracking can also be quite frustrating, as many of the rooms tend to blend together; they don't have particularly interesting features and can thus be hard to find your way back to. There is a map which should make this easier, but in practice it's not particularly useful, as it resembles nothing more than a bunch of squares connected with lines.
On top of the Metroid-esque gameplay, there are also a few other additions. An expected — though ultimately minor — inclusion is the addition of a few new abilities; making their début here are Cupid, Missile, and Smash, which all, regretfully, have since barely made any appearances. The Smash ability is particularly cool, as it gives Kirby his Super Smash Bros. move set and can be acquired from an enemy that might be familiar.
Another addition which is — or at least was — more important is the cell phone, which Kirby can pull out any time to call some friends over; these make their appearance in the form of differently coloured Kirby clones. Unfortunately, this feature is practically completely useless in the Wii U Virtual Console release, as it was largely intended for local multiplayer with other GBA owners.
Originally, when playing multiplayer, each player would get to control a Kirby, and all of them could either work together or go off their own way and do whatever they wanted, even being able to go to completely opposite ends of the game world. You can still summon some AI-controlled Kirbys, but it's just not the same — they're as dumb as a bag of bricks and will rarely, if ever, do what you want them to, which can lead to much frustration. Similarly to Kirby Super Star, this game also includes a few simple minigames, but just like the cell phone these were largely intended for multiplayer, meaning you won't get a whole lot out of them.
One area which Kirby games almost always excel in is graphics and music, and Amazing Mirror is no exception, with the expected cute, colourful characters, locales and catchy tunes. It is largely in part to this usual Kirby charm that this game is still decently enjoyable.
While the Metroid-esque gameplay is a refreshing change of pace for the Kirby series and works well in some parts, it also fails in others. The Metroid games have backtracking as well, yes, but it's not nearly as frequent and annoying as it is here. While the multiplayer features of the original release were optional, it can't be denied that the game was at least somewhat built around the multiple Kirby aspect, making it an absolutely shame that none of those features can really be enjoyed in this release. As it stands, this is still a moderately enjoyable Kirby title, but there are plenty of other, better alternatives out there.