It's widely known that Sonic and Knuckles (S&K) started out as the latter half of Sonic 3, but development constraints forced SEGA to split the game in two, putting S&K onto an innovative Lock-On cartridge that, when combined with Sonic 3, pieced the game back together into its original state. Now, with the announcement that Sonic the Hedgehog 4 is coming to WiiWare and will follow on from S&K's story, SEGA brings us the final piece of the Mega Drive collection.
As the first game to concentrate on different stories for its two leads, Sonic & Knuckles could be seen as a branching point for the series, though its method of delivering story without dialogue was probably something that should have survived into the 'hog's later adventures. As a game in its own right it's competent platforming, but doesn't really get going until you reach the third or fourth Zone, though arguably the same could be said of its predecessor.
Whenever Sonic & Knuckles appears on a console, the first question on everyone's lips is "does it feature Lock-On?", so we'll happily move to confirm that here. Accessed through a menu at any time in-game, you can select from any of the three original Sonic titles you've already purchased and activate the Lock-On feature.
Sonic 1 and Knuckles lets you play a seemingly limitless number of the "get blue spheres" bonus stage; combining with Sonic 2 puts Knuckles into the Emerald Hill Zone and beyond, but Sonic 3 and Knuckles is the series' magnum opus. In fact, it's worth saying you haven't fully experienced either title if you haven't played them with Lock-On.
Joining both titles together creates what many deem to be the ultimate Sonic game, allowing Sonic, Tails and Knuckles to play through the entirety of both games, with different routes for each character based on their unique abilities. Although Tails is again relegated to a facsimile of Sonic's story, with no real path of his own, the red and blue chaps get very distinctive stories, though they play the same levels for the most part.
Sonic & Knuckles's downfall is that it's very much a product of its development: if you've played through it with Sonic 3 locked-on, it never really feels complete without it. Although it is a full game in its own right, it's certainly recommended you grab this and Sonic 3 if you want to experience both titles to their fullest.
Obviously that doubles the price to a rather rich 1600 Points, which may seem steep depending on your existing collection - Sonic Mega Collection for GameCube features seven 16-bit titles and is available reasonably cheaply now too. Plus, importantly for EU readers, the Mega Collection features 60Hz support, something understandably important to Sonic's speed-based gameplay that is sadly lacking from the Virtual Console.
800 Points gets you a decent Sonic platformer that only really begins to hit the heights halfway through, although having separate stories for each lead character extends the gameplay somewhat. Anyone who's played Sonic 3 to death should certainly consider grabbing this to extend the game significantly as it adds new areas and generally improves both titles hugely. As a standalone it's a decent buy, but if you've downloaded previous VC Sonic titles for Mega Drive then this is a true value-for-money purchase.