I abhor ads in and around my games. The thought disgusts me. I find it to be nearly unethnical and to be bad practice, in fact. Or at least, I am against counting on ads as a primary, sought-after source of revenue.
So let's begin.
Comparative to a typical sold game, the exposure:return ratio is very low. I hear typical ad rates are 0.02 to 0.05 cents per click(0.0005 USD) or something to that effect. And what is the cost? Your site is now littered with ugly, disgusting ads. With the accessibility and freedom(of the user to not pay money) of this model comes a cost, and that cost is the aforementioned ugliness joined with the fact you are now stealing your user's time and attention, trying to obscure and distract them from what they came to you for.
I believe that ads bring with them anti-consumer incentives, which is why I abhor them so sodding much. How do you get more ad money? More clicks! More ads! More site visits! Volume! I, as a game developer, am incentivized to produce a mass marketable, manipulative, disgustingly addicting games in order to quite honestly milk my playerbase for profit. I am incentivized to litter my site with more and more ads, and even go to such drastic measures as to include ad videos. That's absurd! That is so anti-consumer, so so so terribly anti-consumer.
I'd rather provide a quality service at a price point. Sacrificing the quality, the sanctity, of an experience and the user's time is disgusting. It's nothing but manipulating and milking them across the board. There is no respect there.
That is why I will avoid supporting the ad market with my games however possible.
Ethics, for the damn sodding win.