Thinking they could repeat the magic of PH was the first mistake. PH working was a fluke--and likely an unrepeatable one. First of all, the stars aligned properly, and you had pretty clear "good guys" and "bad guys" (okay, half the "good" guys were "pathetic" more than "good", but still... there was a clear contrast and sides). Secondly, Dave--while much more on the "pathetic" track than "good"--gave a clear point of identification for some people, as much as we'd like to deny it.
Also, the twists on PH, while occasionally arbitrary, did not remove all sense of control from the players. And producer manipulation, while quite clearly displayed by things like the order people have to pick roomates in, was at least not reduced to cliched clever little reversals on a dime.
PH also didn't create this weird girls vs. guys thing that this show seems to have arrived at. Sure the women and men occasionally had to designate members of the opposite sex for something, but the alliances were more important.
Another thing... and this is almost hard to admit... is that the pure famewhorism of PH--the weird vibe of "we are just here to party and be on camera" was less real than the obvious monetary goals of Eden, but that's actually turned out unexpectedly to be a good thing, not a bad one. The people in PH were just horrible, shallow pathetic people with very little connection to real humanity, whereas the more realistic monetary goals of the Eden people kind of brings them closer to us in a way that hurts more than it helps. Sure, we had "Dave" to root us in some weird disgusting way on PH, but the show also flew off into fantasy-land. These people were cartoons, and thus fun to watch. Eden seems more like an obvious game, despite the absense of intelligent strategy I've already mentioned. It seems crass, instead of simply outrageous.
Of course there's more than the mere failure of repeating PH which made this show so horrible. But that will do for now. It was almost painful to watch, because it seemed so DESPERATE.