The U. S. Congress and the German Bundestag Book

Much denser than Fichte's Jena writings, this is a move from transcendental philosophy to what some would call transcendent philosophy. (This is evident despite that fact that Fichte would undoubtedly deny it). Instead of taking the I of (self)consciousness here, he starts with the Absolute and deduces his famous self-positing I of the Jena period. It moves from an ascending (to the absolute), to a descending (to the manifold, etc.) 'dialectic'.
Most mysterious here is his concept of "light" which appears to be the way in which the Absolute reveals itself to the insight. However, for further clarification, there is an interesting essay in the collection "After Jena" that discusses the "light" in more depth.
There's no doubt that this is a magnificent, frustrating text. It is, to the best of my (rather unqualified) estimation, up there with Hegel's Phenomenology in terms of rigor and power.
However, as the above mentioned essay mentions, Fichte's Absolute is most likely what Hegel would call a "pistol-shot Absolute". Of course, Hegel had no knowledge of this text.