It's difficult to know where to start on a review for Death Note - there are just so many great things to write about!
For starters, the animation is very fluid, and also includes some very impressive camera work; additionally, the characters are all detailed and well drawn. There are also some really nice cinematic touches (in the closing credits for example, it's drawn like an old film roll), and the whole thing is a pleasure to watch.
As the other reviews here state, the story is uniformly brilliant. Without giving too much away, high school student Light Yagami picks up a book (the Death Note) dropped by a bored death god, and, having discovered its powers, decides to rid the world of criminals by killing them all. His actions do not go unnoticed however, and detective 'L' vows to catch the person behind the criminals' murders. The story briefly touches on the morality of what Light is doing, but the main attraction here is the cat and mouse game between Light and the L, with each trying to outwit the other. It's well paced and well written, and crucially has the 'I'll just one more episode...' feeling in abundance. Gripping stuff.
The opening and closing themes were written by J-rockers Nightmare and put the music of most western bands to shame; the incidental music throughout really gives each scene bucketloads of creepy, uncertain atmosphere.
As far as languages are concerned, you have the choice of English, Japanese, or Japanese with English subtitles. As per usual, the Japanese with subtitles is superior to the English dub; however, the English is not as bad as in most anime. The subs are always readable against the backgrounds, and are a fairly accurate translation of the Japanese. The English dub however seems to have been rewritten quite a lot from the original (but not so that it changes the story).
As far as the packaging is concerned, it's in a single DVD box with two discs, each containing four episodes. A nice touch is that it comes with a mini leaflet describing the rules of the Death Note and short plot synopses for each episode. There are some extras, such as the usual clean opening/ending and a behind the scenes feature, and they run for about 40 minutes - a nice addition to an already fantastic package.
Lastly, a couple of notes about the rest of the series. Currently, only the first two volumes are available, with the third being released soon - together, these three comprise episodes 1 to 24. I believe this is different to the American release, where each volume contains only four episodes (hooray for European justice!). The complete series is made up of 37 episodes, so presumably there will be two more volumes released within the next year or so. Since the whole series hasn't been released yet, there's no legal boxset available in any part of the world (including Japan).
Final word? Even if you're not a fan of anime, it's highly recommendable, and I can't wait for the next set of episodes! Amazon cunningly priced the first series at about £8 to lure you in (the next two volumes are around £11), but the series is so good that it's worth any amount of money!