Just found myself watching a video of all the old intros earlier and one thing really comes to mind - the show was not afraid at all to completely change the visual identity of the show year in year out, even two or three times a year towards the end, but they never really touched the theme tune.
Only Big Brother Panto got a remixed version, which was great. Otherwise I think other than a minor change in BB5, plus an earlier change to the break stings back in BB2, the actual theme never changed. Quite surprising how unwilling they were to touch it considering the rest of the presentation - both graphics and in the C4 years the studio - changes every year.
I know BBLB did a feature of remixes each week during BB7 I think, and the final Celeb BB on C4 used a classical remix, but it largely remained untouched on screen. Yes, the original is a classic and perhaps it shouldn't be touched, but even it's creators realised a remix might not be a bad idea and offered to update the theme when C5 took over, but were refused.
It just surprises me how untouched it remained, and a shame that each series wasn't given a more unique sound along with look, especially when themes were used.