It's not quite true to say that Disc 2 features 'the original UK theatrical release'. At least one scene is still missing, so if you're the kind of person who remembers that Leif the Lucky had a bigger part in the cinema than he does on the VHS release, you'll be sad to hear that he isn't any luckier in this version. It is more or less the same as the VHS release, however. But that's not the primary reason for buying this set.
The Director's Son's Cut is shorter than the original - 25% shorter, in fact - and the difference is probably only noticeable to people who know the film well. A line here, a tiny scene there, a bit of running around before he reaches Freya's cave, that kind of thing - it all adds up but isn't horribly jarring in the scheme of things. The film is tighter, and snappier for it. New opening credits are a little distracting, and the impact of the original title screen (and music) is lost somewhat, but it moves the film on a little quicker so isn't a disaster.
The additional features aren't completely inspiring - edited interviews from the time of shooting, rather than new material - but the commentary is interesting, and the packaging is nice. Overall it's a much better product than the previous DVD release of this film, and it's a good fun romp through Norse mythology and post-Python humour, with some lovely visuals.