Not a bad overview, but somehow it doesn't really capture the excitement of the game. The things you (repeatedly) mention as being fun as the fact that your gang grows and changes between games - but it doesn't really mention what's fun about the actual games themselves. What makes it different and/or more fun than Kill-team for instance? It doesn't give a taste of the fact that you're playing as the lowest of the low - scum fighting for territory in the hope that they'll be able to advance within their house and gain respect and power. It just sounds like 40k but with less models.
It'd also be worth describing the gangs in a bit more detail so people get a taste for them, explain what's unique about Spyrers, what makes scavvies or ratskins different to the 'standard' gangs. Explain what sorts of weapons gangs can use, why battlefield weapons like heavy bolters are so prevalent in Necromunda. At the minute they all sound very similar and hence a bit boring. What about special characters, bounty hunters and other hired guns? Maybe mention Kal Jericho and point people at his adventures in Warhammer Monthly on the BL site as inspiration.
You mention the rules are different to 40k and give a few example of how they're different, but you don't mention why and how those differences work well in Necromunda and make it as fun as it is.
Also, you make it sound as if it's quite an expensive game to play, but a starting gang is only about £20 - so you could get two gangs and start playing for less than the cost of a couple of boxes of 40k squads or vehicles.
It'd also be worth pointing people at other useful resources - forums and websites that can give them more information about the game. Is there a Necromunda fanzine?