Funny that this topic is brought up, beacuse this is an issue I am dealing with as a Let's Play narrator right now.
On one hand, I recognise the fact that I have a grating voice and that I lack any sort of sense of humour. Plus, considering the length of even a single mission, I don't have enough material to actually talk all the time anyway. So most of the time while I am playing I remain quiet.
On the other, however, I NEED to talk, since most people are unfamiliar with the type of game I am LPing and that requires at least a certain amount of explanation. Plus, if I do not voice act the cutscenes (even thought I have zero skill in voice acting), the videos end up feeling like they are missing something.
Sadly, I currently few viewers and even they are not commenting, so I do not have any feedback to work on yet. But it is an issue I (and probably every other LPer) encountered and that I am aware of.
Anyway, I personally do sometimes watch Let's Plays. However, the only ones I currently watch regularly are from RanshinDA and AltEisenSpirit. Both are entertaining in their own way.