Ghosts. Not years and years later, but I never watched it until after the final episode had gone out. I don’t know why! When I did watch it I adored it.
The Wire - we didn’t even start it until about five years after it had finished and then we binge-watched it.
Seinfeld. DP watched it when it was on BBC2 in the 90s but I never watched it until about 2010 when DP and I watched the entire box set. We’ve watched it again since then.
To go back a really long way - Secret Army. I was only a young kid when it was first shown in the early 1980s but DP had vague memories of it and bought the DVDs about 15 years ago. I was instantly hooked despite the ‘stagey’ sets and lighting that you get in loads of dramas from that era. So well-written with really complex characters and really unexpected plots with main characters dying etc.