Nice.
Just had a couple of sessions with a thousand or so rolls, and I begin to understand the obsessive grandmas at the slot machines...

The interface works perfectly to encourage hooking behaviour. My favourite way of satisfying the compulsion is drawing for the bigger wins, and controlling the ENTER key (!) carefully to keep rolling at high speed and pausing every now and then to drool over the green winnings.
Despite finding it frustrating to read all kinds of suggestions - because it's impossible to implement every hope of a casual player - I'm inclined to utter my own. BTW if there wasn't a site as great as coinroll I'd just develop it myself to be able to play;

Making the possibility for a second "side bet". That would make it even more rewarding to have one 10000x miniscule side bet, and keep pushing for a high frequency winning main bet half a dozen bets a second until the fat lady sings... YEAH I have found my inner tweaker!