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!
Just expanding on this a bit.... (bitcoinaverage.com):
mtgox 39.83% 847.05 690.0 EUR
bitcoin_de 21.19% 450.60 611.8 EUR
bitonic 12.41% 263.92 602.6 EUR
kraken 11.06% 235.31 610.0 EUR
btce 05.81% 123.49 617.0 EUR
localbitcoins 04.83% 102.69 626.0 EUR