We've been to the Navigator three times now and the fact that we have returned shows that it's pretty decent. The food has been consistently tasty and reasonable value (they have especially good deals midweek) but nothing special. I particularly like their sharing platter to start- great value at £5 each and lots of variety.
On our most recent visit however we were very disappointed with the poor service. We had to really try to get a waitress to come near our table and felt actively ignored at times. At the end of our meal, the waitress failed to bring us our £14 change which was rather presumptive. When asked for it, rather than apologising she looked cross and reluctantly returned the £5 change we asked for. This was disappointing as it put a downer on an otherwise pleasant meal. I realise that it was a busy Saturday night but that behaviour was poor regardless. The service was much better on previous visits.
The atmosphere was good. We were sitting in the bar area and the restaurant section would have better. If going at the weekend then ring a few days in advance to book a table.