The other reviews pretty much sum it up, but I'll put my thoughts in too.
(a) It's a great vacuum. It fills the niche that I was hoping it would fill perfectly: I want to vacuum something small or far away from an outlet, and I don't feel like fetching and plugging in the upright. Suction is great, the tools are great, the canister is great, etc. 5 out of 5 stars for the vacuum.
(b) The battery life is ridiculous. I got 5 minutes of hard vacuuming. The way the charger is designed, it wouldn't even be that easy to keep a spare battery, because the actual charging contacts are on the handheld itself. Come on, Dyson, lithium batteries aren't even that heavy! You could have doubled the power with no problem. You could have designed a backup charger like all the cordless power tools have. 0 out of 5 stars for battery/charger design.
I give it 4 stars overall, despite the battery issue, because I don't ever plan on using this thing for big cleaning jobs. If it's bigger than a 5 minute job, I'll just use the upright anyway. As a light, effective portable that's easy to grab for a specific job, this vacuum is very good.