Mike Grell's Green Arrow became a killer whereas the vigilante in Arrow kills from the beginning, having learned it on the island.
Both the masked vigilante of Gotham City and the hooded vigilante of Starling City are strong, fast and skilled enough to defeat any number of opponents without apparent effort. This puts them in a category intermediate between heroes and superheroes.
In Smallville and Arrow, flashbacks to years ago show the actors as much younger. Is this CGI?
The third last episode of Arrow Season One shows the Queen's Gambit departing and Merlyn's instrument of ethnic cleansing arriving.