Eternal Champions is a sore subject for Sega, I have always thought. The game Sega stacked up against Street Fighter II: The World Warriors (SNES) was the original Eternal Champions. And even though they won't admit it, it was surely a sad day for Sega. But Sega knew what they had. They had a good concept, they had engaging characters ... but it wasn't until they had their Sega CD that Eternal Champions finally found what it was missing.
Sega opted to keep Eternal Champions simple. That is, instead of gratuitous CGI or full motion video sequences so common to prior Sega CD games, Eternal Champions used the CD technology to house more characters, all sorts of secrets, unique game modes, and really some ingenious attacks (some which have still not been rivaled).
It still wasn't Street Fighter II, but Eternal Champions is still a lot of fun to play. The game was one of the first to introduce secret player options into the mainstream. Until Eternal Champions, the most secret characters were 2, or three. But Sega packed 15 extra characters into this mammoth game. And each character had their own story, fighting style, background, and since the game features characters plucked moments before their death, you can imagine the interesting near death story each character has.
And they are extremely interesting characters, too, I mean, there's a politician (who's attacks include flipping his opponent upside down and shaking them for money, and throwing vetoes), a chicken (who throws eggs), and an alchemist who's special move actually changes your opponents controls (something which is never used anymore). Each of the characters is extremely interesting, even if they are novelty.
And if violence is your thing, there are technically four different "finishing moves". Two of the four are character driven finishers, from being ripped apart to having your head removed. One is a stage specific death. In Xavier's stage (Salem Witch Trials) you can knock your opponent into the stake on fire. This was a novelty at this time, and has since been used numerous times. The fourth move is more of a movie. It gives a cinema, complete with early, poor, rudimentary computer animated graphics ... but really, almost all the deaths are much more disturbing than Mortal Kombat, and since that's what they were shooting for, I will given them credit for it.
Everything else in the game is top notch. It just doesn't play like Street Fighter II, nor does it need to. It's a fun game, and has been looked over by Sega on both the Saturn, and so far on the Dreamcast. I would strongly recommend it as the best fighting game on the Sega CD.