There are other online booking sites, most notably Priceline, and also some new entries from TripAdvisor and Google, so there remains competition, and there's nothing illegal or monopolistic about a company being hugely successful, if it reaches that success fairly. But between Expedia and Priceline now, they make up 95% of the market. So what competition there is does seem a bit limited.
The American Hotel and Lodging Association has the same perception. They released a statement that said -- “By approving this deal, only two players control the online marketplace: Priceline and the behemoth Expedia." And then added, "We continue to believe that increased consolidation is bad for consumers and bad for business."