"Must-haves" for me would be digital downloads, and it really helps if it's over Steam, that's much easier than having to manage a dozen download services. I don't mind Steam as a DRM service since it's relatively unobtrusive. GOG is also fine.
Personally what attracts me is generally if the developers focus on the actual game and seem to have passion for it, knowing what they're doing, having an idea of what kind of games heritage to tap(name-dropping Battle Isle instantly got my attention...) and talking about actual game mechanics in concrete terms. The moment the conversation about the game turns to buzzwords, good God I'm out of there faster than you can say my name. Anyone can say they want an "engrossing story" or "exciting mechanics," but if they're not giving actual examples of it, that's all just a scam to me.
Part of this? Show me the game. Don't show me CGI trailers or the developers' faces, show me the game. Show me whatever ultra-early alpha you've got, let me hear a bit of the soundtrack. This is the sort of thing that gets my confidence.
I think the biggest deal-breaker for me, on other videogame Kickstarters has been "celebrity" involvement. The Torment reboot/sequel/revive, Numenera, apparently tried to ride on Monte Cook's coat-tails and, no, I don't like that man or anything he does, so for me, their trying to use his name to get somewhere just makes my bile rise and was what made me have no interest in that(plus their buzzword-storm). Another one I backed out of backing was Portalarium's new Ultima-ish game(Garriott being behind it) when they decided to recruit Tracy Hickman. Obviously he was recruited for his wide resume, but again, he's someone who is, to me, all hype and his writing his terrible. From a business perspective both of those moves are going to invite a lot of fanboys, but from a quality perspective, I consider neither Cook or Hickman to have anything to add.
Updates should ideally always be about the game. Tell us about your vision and ideas as they get narrowed down and nailed down, feel free to tell us about any troubles you're having, any compromises you had to make. I'd rather hear both the good and the bad, rather than just some shiny, polished PR campaign that makes me wonder what I'm not being told.
The rewards I consider most interesting are always soundtracks, I love good music, beta access and alpha access also rank very high since I love "being in on the ground floor," and at a distant third to that would be concept art, which is interesting but has less staying power than music. I rarely find myself attracted to titles or in-game content, but if I have the spare money I'll always go for the higher reward tiers if I really like a project, even without further incentives.