"Felix Zinger"?
Walter Matthau was a pretty good Oscar in the movie, I agree, but then again, he often was really good in those kind of curmudgeonly roles . . . Jack Lemmon, eh, I found his Felix to be a little too obnoxious - not that Tony Randall's Felix didn't have his obnoxious moments, particular in the first season of the series, but I find Randall's Felix to have more of a quirky spunk that makes the character seem all the more delightful in spite of his neurotic tendancies.
Matter of fact, even though I usually have a stronger preference for the more cinematic, single-camera/laugh track-only sitcoms of the period, I feel THE ODD COUPLE really came alive when it switched to multi-camera in front of a live audience. Not that the first season wasn't good in its own right, but both characters feel so much more subdued and restricted in the single-cam format; once they switched to multi-cam in front of an audience, and Tony and Jack had far much more freedom to let loose and play off of each other, it was almost like the difference between night and day: their performances are so much livelier, energetic, and charismatic - Felix, in particular, almost feels like an entirely different character . . . and bringing in the ex-wives, and even occasionally Felix's kids also added a little extra dynamic that was really lacking in the first season, when the ex-wives were always mentioned, but never seen.
It's also my understanding that during the multi-cam seasons, Tony and Jack's method of working together was sort of similar to how Jim Henson and Frank Oz did Ernie and Bert, in that they would more often than not deviate away from the scripts, and act out the scenes in their own way, playing off of each other naturally - or, even in some cases, the writers would just give them a basic premise for a scene, let them do it their way, then tailor the scripts around their performances (i.e. "Oscar teaches Felix how to play football. Okay, go.")