My problems don't have anything to do with acting, pacing, etc. My problem is much more simple: there simply weren't many funny moments. And by "many", I mean more than average. These seems like a reasonable request...I mean, in a comedy, you expect funny stuff to happen.
A lot of people have been giving answers like the bolded statement which are extremely vague and difficult to understand. This isn't directed to you personally as you give a more defined example in the next sentence (though I don't agree that that's funny). I don't really want to talk about "direction" or "charm" any over-arching concepts like that as that's far too abstract and complex. Many of the terms like "charm" are just unsubstantiated buzz words anyway. I'm interested in specific, tangible scenes that people find funny just to get a better understanding of people's rationale.
So, your issue is you didn't find it funny enough, and don't care about any of the other aspects of the movie other than the lack of obvious slapstick moments?
All I can say is that of you don't find Walter Sobchak's rant in the coffee shop when he is asked to not swear so loud funny you probably won't like the humor in the movie. I think that scene is hilarious, and that is not close to the funniest part of the movie. Other scenes that are also very funny are Walter flashing a piece out on the lanes, Jesus' little rant about bush league tactics in league play, Donny's funeral, The Dude doing his detective thing at Jackie Treehorn's house, the shake down of Larry the highschooler, The first meeting between the Lebowski's, The landlords dance recital, The dude buying milk, when the dude reports his car stolen, etc. etc. etc. I could keep going for quite some time. The point is, these scenes are not The Hangover funny, the humor is much more subtle and quirky, as you'd expect from the Cohen brothers.
Different strokes for different folks, but to say that the movie is shallow or not well put together is pretty far out as far as I'm concerned. My best fall back for that kind of critisism is probably the tried and true (but not very constructive) "I guess you just don't get it"