When Cisco was first introduced to us on Arrow before The Flash had even aired I didn't like him but since then he's been fantastic. He can do the serious scenes well like the encounter with Wells but he's also great at the comic relief side of things.
Yeah, at the beginning I was convinced he was going to be the most annoying, stereotypical 'nerd' character. He is still the nerdy character, but thankfully not a one-trick pony so to speak. They really nail the balance for Cisco between silly jokes and the more serious side of him. He's become one of my characters on the show, really didn't expect that.