It's a huge coup for Comcast. Sky has 23 million customers across Europe, and has backed the production of shows for Amazon, HBO and Showtime. It's also well-known for its sports broadcasting, such as its Premier League channel. Comcast will soon have a much larger international presence in these fields. It'll certainly help make up for losing Fox's entertainment assets to Disney in July.
For Fox, however, it's a serious blow. Rupert Murdoch's News Corporation had been trying to snap up all of Sky over the past decade, but the phone hacking scandal at News International (where newspaper employees compromised phones in the name of stories) derailed that effort. After this defeat, it won't have Sky at all.
It's unclear how Comcast's takeover will affect either its efforts or Sky's at this stage. With that said, it's safe to presume there will be some harmonization between the two. That might be good if it leads to easier access to content on both sides of the Atlantic. At the same time, it's yet another example of a mega-merger -- Americans were already concerned about Comcast's size when it bought NBC, and now its empire will span across the ocean.