The problem is not Kraken but the fact there is not much people trading BTC in EUR.
Actually, if we only consider BTC/EUR, Kraken will soon be the first exchange!

Last 24h
Mt.Gox   BTC/EUR   675.000000 EUR   318.1867 BTC   
Kraken   BTC/EUR   607.990000 EUR   316.6295 BTC   
BTC-e   BTC/EUR   613.498000 EUR   170.6412 BTC

Best prices too!