Just so people here know, this version of season 2 is the only one available with the entirety of season 2 on it (apart from the season 1+2 bundle).
The Season 2.0 and Season 2.5 boxsets were only released in the US and contain the first (episodes 1-10) and second (episodes 11-20) halves of the season respectively. Also, season 2.5 contained an extended cut (an extra 10 minutes) of episode 10 which was not televised or included on the Season 2.0 DVDs. These 2 sets also contain deleted scenes from many episodes.
The Season 2 DVD boxset on this page is the UK release and contains all episodes (episodes 1-20) from season 2 except for the original cut of episode 10; we have the extended cut instead, which is a good thing in my book. I've heard that not all of the deleted scenes on the US DVDs are present on the UK one, but the box of the UK version tells me there are just over 6 hours of extras which is more than enough for me.
Now, the only difference between the combined US versions (Season 2.0 and Season 2.5) and the single UK version we have here is that we don't have the original cut of episode 10; only the extended cut, and may not have as many deleted scenes. Other than that, we get the series in one boxset whereas in the US they had to pay for two sets.
I recommend not buying the US DVDs unless you're a serious collector. I also seriously doubt they will release either of the US versions in PAL Region 2 format. So if anyone is waiting for that to happen, do yourself a favour and buy this.
I hope that dispelled any myths the reviewers below me have been spreading.