Like RPGs and Shooters, Action/Fighting games are starting to mix their ideas in order to evolve the Genres. No longer are action games limited to Beat Em Up action, no longer are fighting games Using pallette swaps for their characters in order to save Disc Space. Both have taken on more of a Movie feel. Almost all fighting games have ending movies, unlockable characters, and customizable outfits. While they usually don't have as strong of plots as RPGs and Shooters, Fighters and Action games are known for their replay value and fast pace.
Best Action/Fighting Game
Soul Calibur IV
Most view SCIV as 2008's Main fighter. With Yoda and Vader taking a back seat to a combat system that is equivalent to learning a new language, SCIv is serious business. No Fighting game in 2008 had as many facets as SCIV.
Mortal Kombat Vs. DC Universe
While the concept could've failed miserably, MKvsDC seems to tell the story of each universe well, and it is faithful to both Sides. The Finishing Moves are okay, and there could've been a lot more characters, but overall, MKvsDC is the most infamous Fighter of '08
Super Smash Bros Brawl
While it's not the most hardcore fighting game of all time, it's every game fan's wet dream. We know and love all the characters, the Subspace Emissary is reathtaking, and the super smash's are the perfect thing to move SSB along to the Next generation. If nothing else, it'll be known as the highest Selling Fighting game of 2008.
Super Street Fighter II Turbo HD Remix
For a game that was made in the early 90's. Street Fighter 2 is somehow still around. This is the final version of SF2 (ya, rly.), and it is easily the most satisfying version you'll ever play. The graphics are amazing, the Controls are great as always, and finally, all the characters you wanted are there. Arguably Better than 2009's Street Fighter IV.
Metal Gear Solid 4: Guns Of The Patriots
The only true action game of 2008, MGS delivers it's final epic chapter. If you thought things couldn't get more complicated, you obviously haven't played enough of the series. It's hailed as "The Reason to buy a PS3", and until a better game comes out. I'd have to at least partially agree.
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I was This close || from voting for SF HD Turbo. It is probably the overall best fighting game I've played since Tekken 3, and easily my favorite version of SF, but MGS was 2008 in video games, Snake and Niko ruled '08 for good reason. That said, SF deserves a fuckload of props.