9 year old E91 320d here. Had it about 5 years now, done just over 130k.
It’s been pretty good. By far the best car I’ve owned (although I’ve only been through 5 in 23 years of driving). It’s big enough (just), it’s plenty quick, economy is decent but not exceptional (45mpg or 600miles/tank most of the time). Ride is on the firm/sporty side, although that’s not entirely a bad thing as it does make me think a bit more about how fast I go. Handling is lovely and it’s rare that a B-road blast fails to put a smile on my face.
Reliability has been good. There’s been a few niggly faults – things like windscreen washer pumps and the cabin fan squeaking, but it’s never failed to start and it’s never broken down.
I’ve no desire to replace it – mostly as I don’t really fancy anything else. Same thing with a bigger engine might be nice, but the extra grunt from a 330d isn’t really necessary.