It's been years since I've read any Vonnegut, and I'm not familiar with his entire corpus, but when I read his books, I remember appreciating that he was one of the few authors I've read who had managed to combine serious intent and serious playfulness.  One could argue that that's true of all satirists, but in Vonnegut's case, I think it was his willingness to make light of himself as well as his subject matter that I found appealing.

For comparison (and I'm having a hard time thinking of examples, which probably says how little modern fiction I read), take Roth's Portnoy's Complaint.  It's a satire of middle-class Jewish life, but it's also a satire of stereotypes about middle-class Jewish life, and it's really funny.  After all, the main character (Alex Portnoy) is spotted early in the book fucking a piece of uncooked meat (which goes on to be the family's dinner later, IIRC) in the bathroom, and wallows in guilty terror when he accidently ejaculates all over the bathroom lightbulb.  

That's not really relevant to my point, and I'm not sure why I typed it now, but hey.  Anyway, as keen as Roth's satirical sense is, you're aware throughout Portnoy's Complaint that, while you're reading a very funny book, you're also reading A Very Important Novel, written by an Author Of Prodigious Talent, Whose Work Will Undoubtedly Receive Favorable Reviews In The New York Review Of Books And Garner Him Many Invitations To Swanky Dinner Parties.

There's nothing wrong with writing for immortality, or the approbation of people who can't help but mention Bakhtin in casual conversation, or even for Invitations To Swanky Dinner Parties.  I like Roth.  I really like Nabokov.  I'd probably even like Joyce, if I could ever use my copy of Ulysses as anything but a doorstop.  But sometimes it's nice to be able to read a story that's a really good story, but that's not just fluff.  Vonnegut managed to write page-turners in accessible prose that had something to say about human folly, and human beauty.  And although he witnessed some horrible things in WWII, and struggled with depression for many years, he could acknowledge the uglier parts of humanity and still respond with (a somewhat bemused) compassion.

I suppose not listing Slaughterhouse-Five is some kind of sin, but to be honest, I've only read it once, and at the time, I didn't feel that it was superior to some of his other books.

My favorites are The Sirens of Titan, Galapagos, and Cat's Cradle.  Breakfast of Champions had its moments, but overall was weaker than his other books that I'm familiar with.  I hate not to offer any plot spoilers, but the reasons for liking Vonnegut I've discussed above apply to all of my favorites.

In regione caecorum, rex est luscus.

Which of the six he's had published are you referring to?  You're of course, spot on with your evaluation of "Catch 22" as being timeless, as I can attest that the military hadn't gotten any saner from Heller's WWII to my Vietnam experience.  I'm sure if you sat Iraq War vets down with a copy of the book, they would find entire sections which would resonate with them.

To be honest, the only novel of Vonnegut's I ever read was Cat's Cradle which was okay.  I've seen films based upon two other Vonnegut novels:  "Mother Night" and "Slaughterhouse-Five" but neither of those movies moved me to want to read the books.

Illegitimi non carborundum.

I'd say your liberal peers' high percentage of Vonnegut adulation is rooted in the very fact that Vonnegut was a very accessible writer.  Which isn't to say there wasn't a lot bubbling away in the background, but his stories, at their most basic reading, were simplistic page turners filled with a wry humour that was impossible to miss.  The fact that so very many people could read, enjoy, and discuss Vonnegut's work is the most important point in realizing how beloved he was.  Are/were there better writers?  Certainly.  But when only a small percentage of the population reads and understands certain books, the universal acclaim is harder to come by.

I strongly urge you to read Slaughterhouse-Five.  I know I'm going to dig up a copy and reread the thing, and if the book scans as I remember it, I think your observation about his writing "not aging well" will be proven false.  (Funnily enough, your reservations about Vonnegut are completely in tune with my feelings about Thompson.  About fifteen years ago I realized a writer I'd so admired had shot has wad long,long ago, and while some titles hold up well, the rest of his schtick is tired and trite.  Ah, subjectivity.)

One last thing.  While you might remember Heller only having written one book, he actually authored six, which is a common mistake...because when something really impresses, it tends to shove aside the less-than-stellar stuff.    

I visited Dresden in 1974.  Some buildings were left as they were after the bombing as a monument to the deliberate cruelty of the West.  Some argued that the state (then the DDR- Democratic Republic of Germany) simply didn't have the money to rebuild.

It was a sobering sight, though, to see centuries-old stone buildings burned.