The best thing about “Doctor Atomic,” seen Tuesday night at Lyric Opera of Chicago, is John Adams’s music. The second best thing was librettist/director Peter Sellars’s pre-performance lecture.

It was classic Sellars: passion, humor, fun facts aplenty, outrageousness, and a typical Sellars fashion statement — in this case a colorful vintage shirt combined with a string of beads, and hair that made him several inches taller than nature intended.

Sellars has clearly immersed himself in the world of Los Alamos, New Mexico, in 1946. He knows the people involved in the Trinity test site as well as he knows his own family. (”No one had anything nice to say about Kitty” Oppenheimer, for instance.) I’d read up on it before coming to Chicago, but I learned an awful lot from his talk.

But it may be that he’s a little too passionate about the work, and that the opera could have benefited from a third person in its artistic trinity: a director who wasn’t so completely invested in the libretto. “Opera is the last thing left in our culture that is too long,” Sellars said, arguing against those who want their culture in smaller bites. It’s a good point (said the Wagner fan).

But those who have found this particular opera a lot too long also have a good point. The work is in serious need of trimming; start with General Owens’s calory counting and proceed from there.

Sellars’s message about “the largest program of mass death in human history” is an important one. He’d have a better chance to get it across if he and Adams could pare away some of the parts of the opera that make it harder to focus on the horrors produced by Doctor Atomic and his team.