There's nothing necessarily wrong with Felicity as a character until the writers started shoehorning her into every plot like Lana on Smallville and forcing her romance with Oliver.
I honestly liked her in the first two seasons, just because Ollie never really had a good tech support person or Alfred type of character among his supporting cast before and I couldn't see any of the sidekicks filling that role. But by Season 3, yeah. Tumblr wrote Arrow for the producers more than it's actual writers. Felicity's been fucking awful ever since.