The Kill Team box is exceptionally good value and continues a recent trend, with GW releasing a boxed game containing rules and models for well below the price of buying just the models separately. Some of the other boxes GW has released have only been around for a short time (e.g. Renegade), but they don't always announce if these are limited editions or not. I hope this one stays around for a while.
What makes this set so good is that for once you can get squads for two solid armies, with a good range of upgrade options for both. As well as the figures, you also get a copy of the updated Kill Team rules, which is perfect for new players just starting out their collections. These restrict some of the more insane choices available in larger games, as it only allows a limited range of units and vehicles and the forces are capped at 200pts. The best part for me is that it also includes a mini rulebook for the main 40K game. I would probably recommend this to a new player over the Dark Vengeance box, as some of the DV Chaos units are not the best currently. The DA choices are much stronger, which does not make for a balanced set.
Kill team games are also quick so are very good for younger players. Those with longer attention spans can easily play 2 or 3 games in an evening, which is great for club leagues.
If you bought the old Kill Team rules from Black Library, you can download the update for free, which is also a welcome gesture.