Sonic the Hedgehog 2 (Genesis, 1992)

A great video game sequel ought to expand and perfect the gameplay of the first game.  It should not just be a retread of the same formula, but stay true to what made the original special.  It should iron out the flaws of the original game while avoiding making new flaws.  It isn't very hard for a video game sequel to be better than the original, but there are instances where a sequel takes a major misstep.  On the other hand, you have fabulous games like Sonic the Hedgehog 2 (1992) which are everything I described as a good sequel.
The game basically continues the plot from where the first game left off, with Dr. Robotnic once again trying to take over the world, this time by constructing a doomsday device known as the Death Egg (no, you don't use the force to take it down).  Sonic has a bigger challenge this time, but he is aided by his new sidekick, Miles "Tails" Prower, a two-tailed fox who can spin his tails like a helicopter rotor to fly for a short period of time.  Of course, his name is a not-so-clever pun on the phrase "miles per hour," but I suppose that is forgivable.
Now Sonic has been given one new move for this game, and it feels like a godsend all by itself.  By holding down and tapping the jump button, he can charge up a dash and launch himself from a standstill to running in no time flat.  I can't tell you how annoying it was in the first game to have to run back and build some momentum if you had to get over a slope.  This problem is gone in Sonic 2, and is one of the biggest reasons why it is a much better game.
The other new feature of Sonic 2 is a multiplayer mode, where two players engage in a split-screen race to the finish line in one of four levels from the game.  I usually don't talk about the multiplayer in games because I feel that most games nowadays push their multiplayer in the spotlight while the single player campaign is left to suffer.  Sonic 2's multiplayer doesn't feel that way since the main game is so solid.  It feels like icing on the cake, an additional feature that does not detract from the overall experience.
Sonic 2 also features bigger levels, more of them, and better graphics.  The levels in the first game sported branching paths, but nothing like in the sequel.  There are some areas of the later levels that you may never see if you don't do a little exploring.  They are also more varied and numerous.  The first game had six zones that were broken up into acts.  Sonic 2 has at least twice that.  One level is a marsh with underwater paths and sections high in the trees.  Another level is a giant casino with pinball segments and slot machines, the dark of night illuminated by neon lights.  The game isn't drawn with much more definition than the first game, but Sonic 2 has a brilliant color palette.  Everything is bright and eye-pleasing.
Speed has always been one of the defining features of any Sonic game, but this was the first game to truly use it to its full potential.  The levels are all designed like huge roller coasters.  In fact, this is one of the games used in Sega's famous "blast processing" commercial, where they claimed that Genesis games were faster than SNES games.  This is true, since the Genesis' processing speed is about twice as fast as the SNES' (although in every other techical category, the SNES is superior), and if any game were to be the proof of it, that game would be Sonic the Hedgehog 2.
Like the first game, Sonic can only get the true ending if he collects all of the chaos emeralds, but the way you get them this time is different.  Instead of collecting fifty rings and then going through a big ring at the end of the level, now you need to collect that many rings and go through any one of the many checkpoints in the stage.  This will open up a portal to the bonus round, where Sonic and Tails run headlong down a tubular track, collecting rings and avoiding obstacles.  Collect enough rings, and you are rewarded with a chaos emerald.  Fail, and you are sent back empty-handed, left only to try again next time.
Sonic has become something of a whipping boy nowadays.  His contemporary titles have ranged from lackluster to abysmal.  Who remembers a time when Sonic games were always looked forward to?  His days in the Genesis were a time of constant uphill improvement, rather than a joke.  The Sonic games were always Sega fans' biggest and best argument as to why their system could be superior to Nintendo's.  We are long down the road from those times, but many people still argue as to which system was better.  What's my take on the situation?  Well, Mario has never appeared on a Sega console.