Comment 8 for bug 241736

Fbreader, Sigil or and Calibre can read epub but are not automatically installed (and are not using GTK libraries but I am not sure that it is a problem). And, except for Fbreader that is not really pretty, they are a bit too big to be used as simple readers (it's like using Gimp to view a picture).
It will be a good idea to have it as a plugin in Evince as it is a kind of universal reader installed by default.

There is also the possibility to use an add-on in a browser but it's not really a convenient solution.