MK: Armageddon is (in my opinion) the best in the series.
Plot:
Pretty much self-explanatory, in Konquest Mode you play as a character that is just now introduced in the series; Taven. And you travel around the realms fighting enemies and familiar characters in the MK series to defeat your brother (another person just now introduced) Daegon. After defeating Daegon, you must fight Blaze to save the realms from "Armageddon".
But in Arcade Mode you just basically fight people until you get to Blaze and you win.
Game Play:
Pretty good actually, not any major glitches or bugs, very clean and smooth game-play.
Graphics:
Nothing special, just basically the same as MK: Deadly Alliance and MK: Deception; not really much improvement.
Sound:
Same as any other MK game, a LOT of screaming.
Audio:
Pretty good for this game, I normally am not a big fan on MK's music, but this is actually pretty good.
Conclusion:
MK: Armageddon is awesome. End of story.