Yeah, I was really disappoied in most of the VSTi synths,
The notable exceptions were the B4 and Absynth.
The B4 has excellent organ sounds with leslie effects and the Absynth is great for atmospheric backgrounds. It's got some decent rock patches and the editing features are really tough to figure out but if you're looking for something that's great for providing mood it's awesome. Expensive tho..

Here's some examples if you wanna check out some differences:

Absynth with guitar and drum loops:
http://s93744050.onlinehome.us/mp3/InharmonicMemory.mp3

Halion using factory patches and my guitar sampled to duplicate the electronic version
http://s93744050.onlinehome.us/mp3/RockSplosion.mp3

The cheesy sounds of free synths
http://s93744050.onlinehome.us/mp3/Groovy.mp3