I'm personally a big fan of roulette and slots and I look for casinos that allow me to use relatively small bet sizes (around 0.001 BTC).
If there's a progressive jackpot, that's also a big plus for me, especially if they don't require huge bets to be able to win it.
So let me hear what you are looking for in online Bitcoin casino's...
The first thing I look for in an online casino is, are they provably fair and what games do they have on their website? A friendly UI is a must, but not on top of my priorities since I can slowly learn the website. Other than that, they necessarily must have a good reputation.