The version on All 4 is the HD version which ...
It is not how it is supposed to be watched, the creatives behind the show have universally panned it and if you watch this version and think it's the proper version then Buffy will come away looking like cheap, tacky rubbish.
If you're going to rewatch it, find the correct version. Or at least make allowances that the shots, colour grading, effects and the fact that the occasional camera man is visible is not at all how the show originally aired and judging the show on the HD remaster is deeply unfair.
It is a great show - Joss Whedon was always a dick, and it was always obvious so the 'revelations' don't change much except you might spot a particular plot line and realise 'oh - because Joss Whedon is dick'. Just be ready to give characters passes on the fact they are written by a dick and therefore sometimes say and do dickish things.
Xander is no where near as bad as the reputation he has among fans. He's a teenage boy. Yes, he can be a bit of an ass - but Willow is a power crazed murdering rapist who gives no thought to other people's rights or feelings and the people ragging on Xander being petty seem to let that slide.
If you loved it there's no reason you still won't. You might like a few characters less than you used to - but then you might like other characters more. Back in the day I loved Spike and was so annoyed Buffy couldn't just love him ... now I realise he is stalking her and she is right to reject him. I used to hate Dawn but now I love her.
Angel is also well worth a rewatch - it's a hot mess in places, but gloriously so. It really helps add depth and breadth to the Buffyverse.