Google could be nothing, but disappointment from the way it's built up. It's seen as this magical place where work does itself and things flow so perfectly. The fact is that at Google, most people are going to have to slog away somewhat tedious things like making context ads match their page content 0.1% better. It's not all fun, change the world Gmail and such. Most of it isn't the interesting stuff that we see. That's not really what makes Google, Google. What makes Google what we see is that relentless pursuit of increasingly tiny increases in efficiency. Sure, they had great theoretical ideas like BigTable, PageRank, etc. but what made something like PageRank work was that they didn't stop - they kept making ever more tiny increases in accuracy in a way that could become quite tedious to program and test.
You also tend not to get a full view of things at Google. If you're in backend engineering, that's what you work on. I know that I like seeing the full product and knowing that I've worked on what the users are going to see.
"... most people are going to have to slog away somewhat tedious things like making context ads match their page content 0.1% better."
I'm not sure why you think that the 0.1% improvments are assumed to be a tedious slog. They may have required some seriously interesting new ML techniques just to get that extra boost. Recall the Netflix recommendation algorithm improvement contest that had teams working very hard to get those last fractions of a percent.
You also tend not to get a full view of things at Google. If you're in backend engineering, that's what you work on. I know that I like seeing the full product and knowing that I've worked on what the users are going to see.