The Nokia Lumia 800 is arguably one of the most attractive Windows Phone devices ever released, with a gorgeous monobody plastic housing that is a delight to hold. The curved sides ensure the phone feels comfortable when held, and the entire design screams quality.
The beautiful 3.7" AMOLED display is excellent both indoors and outdoors in direct sunlight. While Nokia's ClearBack technology does make the display very useable outdoors, it does mean there is a slight fuzziness to images that could be offputting for some. Depends on close you look at your screen, and how long you stare at it.
The 8mp camera on the back does a pretty decent job in good lighting conditions, but due to the extremely small sensor on the back of the device it's hard to recommend this phone for the camera included. It's fairly run-of-the-mill phone camera stuff, so I guess we still have to wait for an iPhone 4S competitor.
Oh, and battery life on this thing is excellent. You can easily get a full day of use out of it, but beware of running video or GPS for extended periods of time, as that will run the battery down quite quickly.
While this is your standard Windows Phone Mango installation, the big selling point here is access to a growing collection of exclusive Nokia Collection apps, including a completely free turn-by-turn navigation app, a free music streaming service (which seems to have a very decent collection of tracks), and even a basic photo manipulation app. This collection of quality apps is improving over time, and is a definite selling point for the Lumia range. Neither HTC or Samsung offer this level of exclusive apps out of the box.
Overall, the Nokia Lumia 800 does have its flaws, but really if you're looking for a gorgeous piece of hardware on which to use Windows Phone, with its rapidly expanding selection of apps and associated services, you cannot go far wrong with the Lumia 800. It'll certainly get those around you talking about Windows Phone!