I've been finding that, even though i'm not topping more than $3 a day revenue from my ads right now, i still enjoy the task of seeing my earnings increase and watching the cents come in! I enjoy looking for interesting niches as potential websites i could develop and SEO to add to my earnings. I've been using adsense for well over a year, but only very recently have i started to play with different techniques and tactics to push my "game" along it's all quite good fun!
Yes I also find it to be a game and the score is your earnings. There is not only one score, you can have many: what is the highest day? goal is to earn more than previous month. or goal is to increase CTR on a specific channel for tomorrow by changing ad placement. etc. many games in one and you're winning dollars in the process. Could be said about other online revenue programs.
It is a game when you earn $x/day... but when you start hitting $xxx/day, it turns into a serious business.