I found them intolerable in MGS2 because way too much necessary exposition was delivered via codec and the writing is ridiculously verbose. Kojima always uses 4 paragraphs to say what could have been said in 2 sentences. And just in case you forgot what the hell you were doing after sitting there staring at the codec screen for 15 minutes, they'll repeat it.
Now MGS3 did it much better, less codec convos and the ones that were there were more concise, and more entertaining cutscenes to deliver the story. Plus it was loaded with tons of optional codec convos that gave you background, trivia, easter eggs, tips and character development without destroying the flow of the main game. That's what I missed from MGS4, the optional stuff.