L'Eclisse seems to begin where L'Avventura ended, as an empty and dissolving relationship becomes clearer in the emerging light of the early morning. The film is often an extension of that earlier masterpiece's themes - no surprise since they are the bookends of an informal trilogy at the core of Antonioni's career (the middle film, La Notte, is suspiciously missing from the Collection, despite a lone terrible, now out-of-print DVD release in the US). L'Eclisse stands on its own mainly because of Antonioni's growing confidence in his newfound aesthetic and grammatical structure. Where the mystery of L'Avvenura enhanced the perception of aimlessness at the center of the film by contrasting it with a more conventional premise for a movie, the story of L'Eclisse desires no such counterpart.
The end effect of Antonioni's sure hand is to move away from prose-styled statement into a more flowing poetic structure. This is both appealing in its dreamlike quality (think the more obvious and even more obtuse Last Year at Marienbad from the previous year) and frustrating in the absence of ambition (not in a thematic sense - this is just as ambitious a film as L'Avventura in this regard - but in a meta-cinematic sense). This is not the towering statement about film the earlier picture was, but instead a personal and interpersonal commentary on human interaction. This means people who didn't like L'Avventura are going to really hate L'Eclisse, while those of us who loved that film will have a more unpredictable reaction here. Personally, I enjoyed L'Eclisse a great deal, but I'd put it in the second tier of Antonioni's films, despite another memorable performance from Monica Vitti.
Interestingly, one of the essays here mentions that Bergman considered Antonioni an amateur filmmaker. I assume this was intended as a dismissal of his work, but I think it's an insightful comment that says a great deal about not just Antonioni's output, but Bergman's as well. Like Kurosawa, Fellini, or Hitchcock, Bergman was also an entertainer first - which is not to say he was an artist second, but rather his art had a primary goal of affecting a viewer on an emotional but actively concrete level. Antonioni would never be mistaken for a craftsman, and that's exactly as it should be when it comes to iconoclasts. L'Eclisse might not hit you in the conventional sense a narrative film would, but it has a better chance of getting under your skin and refusing to leave.