Sonic the Fighters is a fighting game originally released in the arcades in 1996, but it later got numerous console ports, including the Sonic Gems Collection and an updated version for the PlayStation 3 and Xbox 360 in 2012.
While it does have a difficulty spike, it's poorly done. The first stage which is always Knuckles, is way too easy as he doesn't block, but the later opponents will always block, until you destroy all their barriers, also not helping that the penultimate stage with Metal Sonic is way too hard.
The final boss fight against Dr. Robotnik only lets you try once.
To play as Super Sonic, you have to reach the penultimate stage against Metal Sonic as Sonic without losing once and win one round to play as Super Sonic in the second round against Metal Sonic. This sounds simple in theory, but is a real pain to accomplish with the difficulty spikes.
Despite being composed by Takenobu Mitsuyoshi of Virtua Fighter and Daytona USA fame, the music is average at best.
There are strangely eight Chaos Emeralds in this game, while in all the franchise it has been established that there are only seven (six Emeralds in the first Sonic the Hedgehog game).
The order of fights is questionable (Knuckles being the first opponent makes no sense given how he's often portrayed having good strength).
The controls are rather hard to get used to.
Abysmal hit detection at times.
Hard to finish combos.
The story is mediocre at best without any proper explanation of what is going on.
The game itself feels more like an extremely simplified version of Virtua Fighter or Fighting Vipers, just with Sonic characters, as it features similar type of graphics and gameplay style.
Good graphics for its time.
The Xbox/PS3 ports allows you to play as Metal Sonic and Dr. Robotnik.
This was the first Sonic game to be rendered with 3D polygons.
There's a secret character known as Honey the Cat, who was an unused leftover character in the original arcade version, but was later added back into the PSN and XBLA versions. Honey would later go on to appear in the Archie-published Sonic the Hedgehog comic.
There's another secret character, which is a car from Daytona USA (Another arcade game from Sega).
There is another version of Metal Sonic called (Rocket Metal) that can be accessed with cheat codes.
Interestingly, some of Sonic's moves in the Super Smash Bros. games originated from this game (although they use different animations), as mentioned in GQ#5.