I got interested in the LP scene some time ago, first with Boatmurdered (A phenomenon many DF players try to reproduce... but there is only one Boatmurdered so far!), then other LPers, like ProtonJonSA, DeceasedCrab, Slowbeef and Diabeetus, most of the old LPers, along with newer peeps like Mangaminx, Northernlion, Michaelfox, etc etc.
And then, of course, there's myself (although I have to take a hiatus, for reasons I won't go into). I try my best to LP the games I play with at least a measure of humour and respect (or, if I find I've lost all respect for a game, like Dragonshard (not shown on YouTube), I'll snark at it over the cutscenes), and, as such, I've basically tried to avoid everything I've ever disliked about YouTube LPs. So I follow these informal rules (mostly)
1) Thou Shalt Not Faff About Too Much.
2) If there is voice, Thou Shalt Not Talk Over It Incessantly.
3) If a game is hard, it's hard. Don't be dissing the section you spent almost an entire video dying on.
4) The game is the important thing. Your opinion is secondary. You, yourself, are tertiary.
As to commentary over post-recording? I honestly prefer commentary. You get to show honest reactions to the game, and, while you do miss stuff sometimes, any LPer will look back over their vids, and mention any cockups they may have made. If not, their fans correct them, and if they ignore that... well, that's no good!
Anyways, TLDR: I LP, of the YouTube LPers, I like lots, including newer guys like NorthernLion and michaelfox, I LP , Runaway Guys and Freelance Astronauts rock, don't be a big wally when LPing yerself, prefer commenting "live".