Nothing bad to say, nor anything good really - they are average.
I have a new set of 255/55/18 on my Td5 and have not found a ditch, lost traction on a roundabout or got stuck on a muddy field.
Maybe I'm lucky, skilful, or just average - but I trundle about quite happily on them!
Would I rather have 16's with BFG's or GG's? - Yes, smoother ride.
Can I afford them? - no.
Happy with what I have then!