I sort of wonder what's going on with me that I felt compelled to pick it up while I was watching Mad Men Season 2 and Revolutionary Road had arrived from Netflix. Something Happened's themes fit right in with the workplace, family and social realist dystopias depicted in those more recent entertainments. Interesting, though that they each take place in different decades. How much changes, how much stayed the same.
As a stream of consciousness work, it was sometimes tough going. A lot of it seemed non-crucial. There's a feeling of descent into madness and depression, but it probably could have been relayed more...compactly. (It does rely on they same narrative 'peeling the onion' that makes Catch-22 so effective). With a 10+ year gap after Heller's previous novel, one wonders if the editors left him to his own devices - possibly at the expense of a tighter, more effective work.
Overall, I'd call it interesting, distressing, but only for those who are really intrigued about what else Joseph Heller could do. I would not recommend this to someone coming to it simply via Mad Men.