We stayed in Kalamaki about 3.5 years ago, the place was lovely, nice restaurants, sensible prices, good selection of bars, friendly locals etc. The bars even had double glazing to pull across the entrance at midnight to keep the street quiet, we loved it. We walked along the beach to Laganas one day and it was chav central, a bottle of soft drink cost about £4, it was full of shops selling typical tourist crap and fast food restaurants. At that point we could've been in Ibiza, Aya Napa, Magaluf etc, the place had no character. I'm being hypocritical considering I used to go on such holidays, but I really hope the clubbing / boozing croud get bored of Zakynthos and leave before it loses everything that's good about it.
Oh, and enjoy your holiday