Buso Renkin, Alchemy Arms: 7.5/10
Pros:
Maintains a well thought out plot.
Has extremely funny moments, though there are very few.
Fight animation gets more detailed over time.
Cons:
The few plot holes there are tend to linger.
Parts of the ending that contradict other crap.
Overall it's worth a watch, but I don't think I'd really watch it twice. The English Dub is passable, but feels over acted or under acted, its hard to tell which at times.
Also, if Venture Bro's wasn't enough to satisfy your urge to watch Butteryfly themed Antagonists this will interest you.