All Let's Plays you're likely to find through a google search are really, really, bad. The Pewdiepie style of doing them is terrible but inexplicably popular with millions of children, and they're so easy to churn out that youtube is flooded with low-effort ones.
Most serious let's players hang out on SomethingAwful's let's play forum, make videos filled with nonstop insightful commentary, and languish in obscurity.
I watch some comedy LPs where people play a really ridiculous game like 50 Cent: Blood on the Sand and make jokes.
I also watch a lot of LPs where someone really knowledgeable and skilled plays a game to 100% completion and shows off everything.
They're mostly useful when I want to see a game but have no interest in actually playing it myself. Incredibly hard games, games with a mechanic I just don't enjoy like stealth, etc.
Here's my recommendation if you want to see some quality LPs: http://chipandironicus.com/videos/index.html