The big thing about Let's Plays is if you feel like you can have fun with it and are willing to put real effort into what you're doing. I, personally tried to do a let's play and had a lot of fun with it until technical difficulties broke it.
I still have a few pages worth of notes hanging around somewhere...
Really, though, there are many types of Let's Plays, most usually: Player reaction LPs, documentarian LPs, and role-playing LPs. These usually intermingle with one another, though here are a few examples to demonstrate the extremes: The reactionary, the Documentarian and the Role Player.
There are also two primary formats: Video and screenshot. Video often best represents action games, but can work well with turn-based or more slow paced titles. Screenshots lend themselves most to turn-based and slow games, but have been shown to work adequately with most genres, other than beat-em-ups and shooters.
I find the generalization that the only quality LPs are the documentarian ones false, but understandable. The main reason being is that people who are teaching the game are putting more effort into their LPs. Its easy for someone to put a video camera up to their TV screen and do a terrible video, saturating the LP arena, as is said. However, this is as rational as saying that all hamburgers are bad because most come from McDonalds. A hamburger will never be as "sophisticated" as a quality cut of beef, its enjoyable on its own merit if you can find a good chef.
And even if you aren't necessarily all that original, you are still something. If you can appeal to a certain niche Let's Play audience, there's no harm in it. I mean, I love the LateBlt/Hercrabbiness/Lucahjin/FireWizard23 Adventure game LPers and would love to see more videos like that, even though most people find them terribly dull.
Still, before you begin to Let's Play, I urge you to look beyond Youtube before making your decision. On Youtube, you're a lone individual, with nothing but your ten-minute videos to place at the mercy of its questionable community. Here, on the Escapist or another internet community, you could follow the Something Aweful's example of making a thread to host the Let's Play and act as the heart of its discussion. Also, consider alternative video upload sites, such as Viddler or Blip.TV. These allow for a longer video and provide a different level of audience interaction, which may or may not be what you need.
Of course, there's always the Screenshot format, which is eclipsed by video LPs due to a common misconception in the Let's Play audience that LP's are exclusively a Youtube thing. While technically simplistic, it requires a different toolset than video LPs and can be demanding on one's writing abilities. If you have a charming writing style and a slow game, this could very well be your ideal medium.
