I have a Dark Energy and I like it a lot. Really glad I bought it. The range of the LFOs is great (super slow to super fast) and the basic tone is good. It can sound nasty or smooth depending on how you tweak it. As vvd mentioned you can also use it to process other synths and drum machines. I use it for basslines, drones, leads and effects and it's effective at doing all of those.
Some good Dark Energy Videos on youtube, they show the range of sounds it's capable of:
Also have a look at the Vermona Mono Lancet, the Analog Solutions Semblance/Telemark, the MFB Kraftzwerg, and the new TomOberheim.com SEM. They are very similar to the Dark Energy featurewise and all of them (including the Dark Energy) are good so you can't go wrong.