It’s more of a string of events accompanied by a whole bunch of miniseries, most of which are needed to get to know the characters (or their new interpretations) and make sense of the story.

The rough idea is that it started with the eponymous Thanos 12 issue series, where the later 6 issues directly lead into the Annihilation event and its sequel Annihilation Conquest. Nova (Richard Rider, who is the led character) got his own series from that (Nova vol. 4) and a team that forms the basis of Guardians of the Galaxy forms in Conquest. Those two series ran concurrently and tied to the subsequent cosmic events War of Kings and Real of Kings. The whole cosmic run was somewhat tied up in Thanos Imperative and Annihilators miniseries and basically ended.

The the GotG movie happened and Bendis started writing it and it just wasn’t the same. There might be good stories after that, but I lost interest at that point.

The good thing about this whole thing is that it’s taking part far away from Earth and thus is not tied up with the mainstream Marvel continuity in any major ways (Annihilation takes place during the comic Civil War) and the bulk of the characters are forgotten or unpopular characters given modern interpretations and put in a different context than usually, so you don’t really need to know much about their history, since their characterisation is being built up, almost from scratch in some cases. And it’s awesome. Like the Super Skrull fighting in a war against a galaxy-ending threat and being super powerful instead of jobbing to Fantastic Four like he usually does.