Its not obnoxious now because uBlock and spam filters works so well, and HTML5 killed Flash. If you don't take such quality filters into account, advertising is far, far worse nowadays.

We're talking about everything before the dotcom boom here. The internet was a lot bigger than WWW, and Macromedia Flash (and Doubleclick) were initiated in 1996. That covers less than 5% of the 20th century. Also, Flash wasn't (ab)used right away for advertising, and if one didn't have it installed not much was missed. Perhaps an online Flash game or two didn't work. No big deal. There was spam on Usenet (the first spam coming from Digital Equipment Corp or was it SUN in the early 80s) and IRC, but it wasn't acceptable.

We're talking about 5% of the 20th century because for most people the internet was only available for around 5% of the 20th century. Doubleclick wasn't the first ad network.

There was acceptable advertising on usenet too in the form of signatures.

Not for the first couple of years of public early-adopter access during the mid-90s.

The first couple of years were a glorious outburst of creative kookiness and cultural insanity.

Then the spammers, scammers, and MBAs moved in. And here we are.

Spam goes back to the 70s.

On the web side I remember back to at least 95 pretty well and there were banner ads everywhere. I had a homepage with like 3-4 web ring banners on it + the ads from Geocities themselves.

A quick look says the first banner ads appeared in 1994 and the first paid ads in 1993.

I think you're probably looking back with rose tinted glasses.

Well yes, there was a period of time during the 20th century when all commercial activities were banned from the internet, until around 1995 IIANM. Basically Internet was non commercial from about 1978 to 1995, though I think the first banner ad came to existence 1 year before in 1994, that's still a longer period without ads than with.

If you look at archives of USENET from those time periods plenty of people had ads in their signatures for example and even if you don't count that the first spam message was sent in 1978 so that whole time period is post internet ads.