Mortal Kombat Komplete Edition that I bought on PC from GreenManGaming about a week back - they were selling it for ?8 and I had ?2 credit.
Best fighting game ever. Never before have I found a fighting game that marries awesome, bonecrunching gameplay with so much content. You have an extensive Story Mode, an extremely long 'Tower Challenge' mode that is fun and helps you learn the various characters' moves. Following on from that, you have a comprehensive Training Mode and when you've exhausted all that you can either grab a mate and battle one on one, or you can form a tag team.
There's the excellent 'Test Your Luck' mode, where a slot machine style set of reels will spin and saddle you and your opponent with random advantages and disadvantages, such as 'Vampiric Touch' (any hits made on your opponent will regenerate your energy while draining theirs) 'Headless Combat' (which removes both combatants heads, leading to extreme disadvantages if you're playing as Kung Lao for example). Iceballs or Meteors can rain from the sky, and a whole plethora of other things can happen.
And once you're done with all that, there's the inexhaustible supply of fun to be found online.
Of course - how could I forget the infamous Fatality moves, or the hilarious 'Babalities'?
The fighters are varied in their looks and fighting styles. You have robots, reptiles, demons, as well as humans. If you want a fighting game on PC or console, don't overlook this gem.