Exterminatus Now is some drawfag's unholy combination of WH40K, and his Sonic OC's. As you might imagine, it's very, VERY stupid.
To be fair, while many are scared away by the whole 'Sonic + 40k' thing (which you certainly wouldn't be blamed for because the concept smells heavily of bad fanfiction) the comic is surprisingly not the worst thing ever. The art and writing are both pretty solid at least (although the writer seems to be terrified his readers may one day forget it is a British webcomic). If you can let slide the fact that that is a rat in an Inquisitor coat over there you'll find there are far worse things to read.
This comic has stopped updating as the artist got tired after 500+ pages. Not mentioned above is that it has some of the most quotable and hilarious lines/conversations akin to poor shooting and the ensuing massacre.