I don't love the design, but I think it worked conceptwise. This was a hybrid of Parallax and Legion. It was dirty, excrementous, smoky, tentacled cloud of fear and pretty much just disgusting. The faces were fantastic, and effectswise, it was pretty solid.
The thing sucks the fear/souls out of innocent people. That's a pretty horrifying concept. It infected Hector Hammond with fear, and look what he turned into.
The shot where it's pouring into Coast City and crowds are running from it was pretty fantastic. It clearly has some serious power. We're never told it can't be hurt, just that fear is a powerful energy.
We're told it destroys worlds, and the scale of destruction is hinted at. We see what it can do to Green Lanterns. I think Parallax was a credible threat, just not a very deep one.