We had the previous model to this (the nn477) and that has been a complete pain. Noisy, unreliable (2 breakdowns in 4 years), seemingly inefficient at times. Luckily we took the extended parts and labour insurance policy so when it finally became "uneconomic to repair", we were able to reconsider our next purchase with a little head start on funding.
Reading some of the negative reviews here, I strongly suspect others had the nn477. It looks identical but is so different in operation.
Our new nn479 is so quiet, with no fan run-on after heating. Heating is much more efficient, consistent and in keeping with its "E" rating.
I did loads of research on our options. We need a good family sized capacity with easy cleaning of stainless steel interior, did not want a combi/grill, and reliability was important. The combi equivalent of this model was indeed tempting, but unless you only cook jacket spuds it sounds like there are big issues when using the grill/convection functions.
On balance this 27L Panasonic still top the leader board.
In fact the engineer who came out to see us pretty much said they are still the best, but that a few years back they tried to add too many whistles and bells which may have caused problems around the time we bought our failed unit. Have a look in the likes of John Lewis (who tend not to stock any rubbish) - they mainly stock Panasonic.
In terms of value for money, this one is hard to beat for a straight microwave. Time will tell whether they have solved the reliability issues, but so far we're very pleased with the upgrade.