I was surprised by the fact the show isn't dark, brooding, etc. Even got me to start watching Arrow.
Then came Captain Cold. Really smart. Check. Code vs. Killing (in his opening scene). Check. Not metahuman. Check.
Then as soon as he gets the Cold Gun (lethal only) he goes on a killing spree. The writers basically said "we can't write interesting villains, so we'll just write violence."
I want to like the show, but turning the leader of the Rouges into a psycho killer is atrocious.
Interesting note: Captain Cold (tech-based, does not kill), Mr. Freeze (tech-based, kills only as a last resort), Icicle Jr. (meta, stone killer), Killer Frost (meta, name says it all). Only exception to the meta/tech-killer/not seems to be Ice of the Team Formerly Known as the Justice League.