I'm talking about that effect in fighters and beat em ups where everytime you hit someone hard (or even moderately) the game pauses for a few frames to accentuate the hit. Or in NSMB when every other player gets paused for a sec cos P2 died or picked up a mushroom.

Am I the only one who finds it incredibly annoying and disruptive to the flow of the play experience?

I feel exactly the same. I hate this effect and just like you said it's disruptive to the smoothness of a game. Why to bother with 60fps when you then use this shitty effect is beyond me.
For that reason I loved GoW games because they lacked it. But it seems it is present in GoW A which annoys me.

In 2D fighters I can appreciate it but in Mario, fuck no.

I think it's more annoying when it's not on purpose.

I agree it can be annoying, but it does depend on the type of game

You shouldn't play Castlevania Lords Of Shadow, its annoying as hell, and even more annoying on Xbox (it lags after slow mo) , and the slowmotion is after every kill.

I don't mind it in Zelda but it is annoying in NSMB as I have died many times because of it

I can't think of a single instance I didn't dislike it. Seems to me like just a bad idea in general rather than an issue of whether it's executed well or not.

yeah it can be quite frustrating in Mario games.
I'm not bothered by it in other games though.

Yeah, but when it happens all the time during play.

Depends; both have varying degrees of annoyance for me. I guess when its intentional it gets to me more because it's I can't fathom why they would think it's a good idea.