Arrow - Spoilers galore
The producers have been a bit dismayed at Arrow's ratings, especially in comparison to Flash, so they thought they'd make Arrow a little more 'lighthearted' like Flash.
What they don't get (producers never seem to truly understand their audience, IMO), is that a lot of people watch Flash because of the 'fantasy' nature of metahumans, etc. Arrow, on the other hand, is grittier and darker. Unless Arrow grows some superpowers (god forbid) the show will never be Flash. Two different shows with two different meanings and two different types of appeal, IMO.