I agree with those who are saying that the gambling angle feels forced. HBO is incredible at character develpment and depth. It's one of the reasons that some people who are more casual Soprano fans will watch an episode and find it "boring" - often times, I've found, they feel bored because they are not as invest in the characters as people who have watched it religiously. When you're as into it as most here, you're simply interested in seeing where each character goes, what they're thinking, and ultimately, in most cases, what will be their downfall. "Action" is not always required.
I've always felt that Tony was not a gambler. People here have said that he has "always gambled" but I don't agree with that. He'd play some table games at the casino he gave to Tony B., and on some occassions he'd play hearts and whatnot. But he never sat in the big poker games. He never laid a serious sports bet in the entire show, if I recall correctly. Gambling, simply, has never been a hobby of his. If I'm mistaken in this, please let me know - but, and I've referenced this before, I remember a flashback Tony had about when he saw his father beat up the local butcher, and later his father explained that it was because he (the butcher) owed him money and could not pay. He then lectured Tony about the vices of gambling and said "You should never gamble."
In my mind, Tony has always been the lender and the collector - the guy who capitalizes on the gambling habbits of others. He was always in control, on that side of the gambling dynamic. While I understand that character definitions are not so rigid and are able to change and grow, and this is clearly a sign that Tony is losing control over things, it really does seem like an out of the blue change in what I thought was one of Tony's core values.
I could be wrong, but that's always been my opinion on Tony and gambling.