I’m looking for a single word to refer to an abundance of ads/advertising in a negative way.
“That website is so annoying due to its ___”
“If we put any more ads on this page, I’m afraid we’ll have ___”
The only possibilities I’ve come up with so far are phrases, like “ad overload” or “ad blitz” (the second of which doesn’t have a negative connotation anyway).
A made-up word with a clear intuitive meaning would also work.
I think a key question for you is why you’re complaining about the ads: Is it because of their visual appearance? Then, as @Cascabel noted, you can use cluttered:
Clutter: A condition of disorder, or a lot of objects that are in a state of disorder
This certainly has a negative connotation.
If you’re objecting to the ads solely because of their commercial content, you might want to refer to the impending commercialization or overcommercialization of the site. However, clutter might still work here too (things being in disorder because of unrelated content).
Another option is monetization. From Wikipedia (emphasis mine):
The term "monetization" may also be used informally to refer to exchanging possessions for cash or cash equivalents, including selling a security interest, charging fees for something that used to be free, or attempting to make money on goods or services that were previously unprofitable or had been considered to have the potential to earn profits. And data monetization refers to a spectrum of ways information assets can be converted into economic value.
Still another meaning of "monetization" denotes the process by which the U.S. Treasury accounts for the face value of outstanding coinage. This procedure can extend even to one-of-a-kind situations such as when the Treasury Department sold an extremely rare 1933 Double Eagle. The coin’s nominal value of $20 was added to the final sale price, reflecting the fact that the coin was considered to have been issued into circulation as a result of the transaction.
In some industry sectors such as high technology and marketing, monetization is a buzzword for adapting non-revenue-generating assets to generate revenue.
Although I’m not sure this term gets across a pejorative sense.
In a tongue-in-cheek sort of way, you could also use the old term ad nauseum, as a double entendre:
"That website is so annoying due to its ad nauseum."
"If we put any more ads on this page, I’m afraid we’ll have ad nauseum."
(make sure to accompany these statements with a nod and a wink)