I've only just had the chance to watch this so my thoughts...
The opening scene worried me as it was basically a rip from series 3 but from then on I felt a sense of relief. Series 7, 8 and Back to Earth were all poor imo and this was generally better. Getting back to the 4 main characters was certainly a good move and the writing was mostly ok. One or two decent jokes and nothing as cringeworthy as some of the stuff in the past. Chris Barrie also proved that he is still a very fine comedy actor.
However, I would agree that a lot of it was very predictable and old-fashioned. If it had been a new sitcom then I probably would have judged it more harshly as I didn't find myself laughing often enough. Something about the tone and the pacing of the episode also seemed wrong. The scene with the simulant was far too rushed and it didn't work and the tone felt more pantomime than any of the first 6 series.
Overall though not too bad and not too good.