This illustrated chart by H. Caldwell Tanner shows how much time is needed to properly enjoy each genre of video game, from casual games to epic length RPGs, and in my opinion it pretty much sums up what all hardcore gamers know-each genre has a different level of commitment, and appeals to a particular type of gamer.
This chart is a great way for newbie gamers to figure out what kind of games they're looking for, instead of borrowing your copy of Mass Effect 3 for six months just to discover that they don't really like RPGs.
Link --via Geeks Are Sexy
You average casual tablet game is fun for a few hours. But the games that require more time to learn often provide many more hours of play.
And then there are the games like Valkyria Chronicles, which takes about 15 minutes to learn the basics of, and provided probably 40 hours of fun on the first play-through alone.
The only RPG I've played was Baldur's Gate. That took way, way too much time.