My wife and I paid a visit in May / June. We missed the signs in Loughborough and ended up at Quainton Road instead but that was probably just as well as I suspect the parking is easier there? We arrived late-ish in the afternoon so we really only had time for a return trip to Loughborough. Oliver Cromwell was running that day but our timing meant that we literally saw it "in passing".
It is certainly a different experience travelling a double track line rather than a single.
Whilst there was nothing "wrong" with our experience, I don't think we will be rushing back. It's quite a long way from where we live. Other choices for us and we have been to them all recently are Watercress, South Devon, Bluebell and Severn Valley. My favourite is still the SVR but that's quite a trek too. Why the SVR? Partly it was the first preserved railway I ever visited back in the late 70s, and partly because there seems to be a lot to do.
David