I personally love the book. It gives some very interesting insight into various topics of Tolkien's Middle-earth.

As for the action, there are two major chapter featuring battles in quite some detail (perhaps more detailed descriptions than the battles in the Lord of the Rings): The Battle of the Fords of Isen and the Battle of the Gladden Fields.
Furthermore, Tuor's coming to Gondolin is described, as is the story of Turin Turambar, the Island of Numenor, Aldarion and Erendis, the Kings of Numenor, the story of Galadriel and Celeborn, Cirion and Eorl, The Quest of Erebor, The Hunt for the Ring, The Druedain, the Istari and the Palantiri.
In the Cirion and Eorl part, there are some battles between the Gondorians and the Wainriders, but the other parts are often without many battles, or with only references to them. Some characters, races and items are more explained though, which I find really interesting. Furthermore, Christopher Tolkien gives notes, and commentary on his father's work and how his works changed in the course of his life. I think the Quest of Erebor part has some 3 or 4 different texts, nearly the same, but emphasizing different things. That story is also unfinished in the sense that Tolkien never wrote a final, all enclosing version.

So yeah, there are some battles, but it's mostly a more detailed view on some matters, and it also sometimes compares different manuscripts.