These were: uncluttered search-only, instead of a portal filled with junk; no paid-placement; it was also faster due to clever backend, so an acquirer could save money on the backend, bringing it down to adequate speed.
Some argue that The Algorithm (pagerank) wasn't important for google's success at all, except as marketing to geeks, because search results were comparable to alternatives.
Today, apart from consumer habit, google's biggest advantage is speed, possible by massive capital investment in datacenters.
But also today, google is hamstrung by money (Wall St), making them vulnerable, as previous search was.
OTOH the problem/need was there, maybe eventually there would have been another google targetting search-only.
As an early user of Google I vehemently disagree. That better results was not due to PageRank alone is well understood.
Google was just fast and ad-free, unlike AltaVista, which was ad-infested and slow. That was the attraction for myself and the other people I knew who used it.
Getting the top quieries right is relatively easy by hand, the real question is how the engines performed on random queries.
Perhaps, like judgement day, Google was inevitable.