Good ads do exist ... but yes, 99%+ would not fit the term,
Back when Opera web browser had for pay licenses (which is to say, before 9.50) you could use the browser for free if you didn't mind an ad banner in the top-right corner. And in the later of the pre-9.50 versions you could choose whether to see the standard random ads or contextual ads - the latter were provided by Google based on the page you were looking ad and were text only. (Only for non-secure pages, they weren't going to tell Google what secure pages you visited.) We had a number of users who would pay for the license but then not enter the code so they could continue to see the contextual ads, and of course since the ads were consistently placed and unobtrusive if you weren't interested they were easy to ignore as well.
Mind you, we had reports of some websites specifically blocking Opera because in their minds Opera's ads were reducing the value of their own ads ... but this discussion isn't about ancient web browsers.
A good ad is one that is interesting to the people who see it (as much as possible anyway), that is unobtrusive to those who aren't interested, and advertises something they are likely to be interested in. (The ad I'm seeing below this box for a local financial institution is not particularly good as financial institutions are not something you're looking for that often, and it isn't really unobtrusive either.) These websites where half the page is ads - forget it. Video ads? Only embedded in other video content, and even then not usually. Ads that jump up when you move your mouse over something? Never. Click on perhaps, as the user indicated interest, but not move over.
And if you're Google (or any other ad network), the ads should be governed by interest to the user rather than how much the advertiser is paying (well, as much as feasible anyway). People won't click on it - and are more likely to block it - if it isn't something they want, so it doesn't matter how much they are paying. Doesn't matter that they bought some keyword if it isn't appropriate.
Is that really so hard to understand?