The Final Fight franchise has had a weird history. Despite the success of the original arcade game, two classic SNES sequels, a truly startling amount of memetic impact on Internet gaming culture (at this point, I'd imagine more people know about Mike Haggar from online humor than from actually playing any of the games he was in), and a big chunk of the cast migrating over to various Street Fighter games, the series itself has gone almost nowhere in the last twenty years.
Every so often, Capcom tries to dust off the IP and do something with Final Fight. They tried making a fighting game out of it, Final Fight: Revenge, the last American game released for the Sega Saturn. It was a disaster. A few years ago, they tried to update the game for modern audiences with the gritty, Frank Miller-esque Final Fight: Streetwise, and that sank like a rock. So far, the most successful Final Fight games since the third SNES title are ports of the original game, which show up all over the place at irregular intervals.
Double Impact is one of those ports, with the original Final Fight sharing a double bill with the somewhat-more-obscure Capcom sidescroller Magic Sword. Both games come with unique unlockables and a host of extras, including remastered music, concept art galleries, and the ability to screw around with the visuals to make either game look like they're being played on an old arcade CRT monitor.
It's important to realize here, however, that for all the ports of Final Fight that there've been over the years, this is the first one that's a straight port of the arcade version. Up to this point, home versions of Final Fight have typically been heavily edited due to hardware concerns or half-assed censorship. All the bosses have their original names, Roxy and Poison are wearing their original risque outfits, all three main characters are in the game (Guy was left out of the SNES port), and two-player co-op is available.
Final Fight is a late-eighties arcade quarter-muncher, and was popular enough at the time to start a whole series of similar beat-'em-ups; like Street Fighter II, it founded a genre around itself. Playing it today, it's a good reminder of how essentially unfair arcade games used to be. Final Fight is mostly there to extort one more quarter from you over and over again, and the enemies constantly land cheap hit after cheap hit on you. Bill Bull or Andore run in from offscreen and knock you down before you know they're there, bosses like Abagail have inescapable holds that end in a 50% damage throw, the beginning of the industrial-park stage involves flames shooting out of the floor that are nearly impossible to dodge, and the final boss brings a crossbow to a fistfight. Most of the achievements/trophies in Double Impact involve getting through a stage while "only" losing seven to nine lives, or "only" using twelve continues, which should tell you all you need to know about it.
Co-op is still the game's saving grace. Friendly fire is on and cannot be turned off, as far as I can tell, but the game is tuned around two players. One-player mode is an exercise in frustration, particularly in the later stages when it's you against five to seven enemies at once. Playing it with a buddy is a lot more fun, especially when you're accidentally and constantly knocking each other over.
The second half of the double bill, Magic Sword, is considerably more obscure. It got an SNES port near the end of that system's life and has shown up on a couple of Capcom's arcade collections, but it's not one of the games you hear much about.
It's a shame, honestly, as Magic Sword is pretty good; it's fast-paced, well-animated, challenging without being ridiculously unfair, and has a cool gimmick. As one of two generic sword-swinging barbarians, you beat monsters with your sword and occasionally find a magic key, which you can use to free prisoners throughout the magical labyrinth you're attacking. Each prisoner works like an option from Gradius, adding an extra attack every time you swing. It all reminds me of nothing quite so much as one of the earlier Metal Slug games, with the same heavy focus on pattern memorization and twitch reflexes. It's a great deal more fair than Final Fight.
Magic Sword's biggest problem is that it's a marathon race. It covers about fifty-one very short stages, with a bunch of hidden treasures, secrets, traps, and bosses scattered at random throughout. Sitting down and playing through it in one setting is a repetitive slog, but fortunately, the Double Impact collection features an auto-save.
Double Impact is a good package, featuring two of the greatest co-op arcade games of all time. Final Fight is really showing its age now, but it's been twenty years, so that may have been inevitable. Magic Sword has aged a great deal more gracefully, and of the two, it's the one that I've been going back to.