This is a really a combination of a small child in my life and moving away from where my gaming circles lived. (To this day, I'm not sure if that's a remotely bad thing. It has let me focus on being a parent.) I doubt this is a forever thing but I hope that I remember the lessons I learn from this time.
It has also helped my interest in micro games and print-and-play but that's a long series of blogs in and of themselves. Heck, the rich variety of good games that that a half hour to forty-five minutes is fodder for tons of blogs.
Truth to tell, some of the basic building blocks of the modern hobby fit that time frame. Carcassonne with no expansions, Ticket to Ride, Bohnanza, Ra, Dominion all come to mind. Heck, back when I was playing Settlers of Catan and Puerto Rico on a regular basis, we'd usually polish off a game in less than an hour. (Twenty minutes is the shortest I've ever seen a game of Catan but the winner's dice were on fire like a star exploding.)
One of the big lessons I have relearned is that a game that fits into this time frame can have just about any mechanic, have a solid theme and be full of interesting decisions and tension.
To be fair, while I've been using the term casual game to describe a shorter time frame, some of the games that fit into this time frame aren't necessarily light or simple. Some of them can involve some serious play.
There are actually games that fit into an even shorter time frame that are still surprisingly heavy. While I'm not a big fan of TAJ, a five to ten minute game about adjusting the prices of rugs, it has a surprising the intricate framework. And that is just the first example that comes to mind.
However, I do think that the game taking at least a half hour as a certain degree of heft to the experience. Playing a game that lasts around forty five minutes feels like I've really taken the time to play a game. Had a meal instead of just a snack.
In actuality, the number of solid games that fit into this time frame means that if I never get back into games that takes hours to play, I would still have a very rich and varied gaming life :D