I won't comment on the quality of the show, besides that it's great. I assume if you are buying this season 4 DVD set, or are thinking about it, then you've seen all previous seasons and enjoy the show thus far.
I picked up this DVD set at a store that was selling it early, so I'm able to comment on its contents first hand.
For those who are new to the show, or are trying to catch up, this season 4.0 box set only contains the first 10 episodes of season 4 (which make up the first half of the season (the second half will commence January 16th, 2009.)) This style of packaging is similar to what they did with season two (the entire season is purchasable over two box sets: Battlestar Galactica: Season 2.0
and Battlestar Galactica: Season 2.5
They will no doubt release a 4.5 box set later in the year.
Also included with this box set is Battlestar: Razor (which can also be purchased separately: Battlestar Galactica: Razor (Unrated Extended Edition)
.) This is great if you don't already own Razor.
Overall, it's a great box set. The lack of the second half of the season is made up with the bonus Razor disc (which isn't so great if you already own it.)