People calling Dark Cloud or any other game a Zelda or Mario killer are...given that certain game more hype then it deserved. Now, that game has to live up to the quality of that certain game which, more times then not, not live up to so and so expectations because it was called "certain AAA game" killer. Still, like in the case of Dark Cloud, could be a good game on its own right, just not to the point of that previous game.
As for these Xbox games, they look okay. Nothing mind blowning (and certainly not PS2 beating). The platformers do not even look as good as either Jak and Dexter or Ratchet and Crank. They could still be good games, but not a killer app if you know what I mean. And the fighting game does look interesting (though the fighter names, "Firery Phoniex"? Sounds pretty gay).