The first 3 seasons of TBBT were pure gold, season 4 was an amalgum of gold and silver, but right from episode 1 of season 5 there has been something not quite "right". The pacing seems to be off and and I just don't laugh as much.
However, regardless of how much anyone may criticise season 5 it is several orders of magnitude funnier than any other sitcom currently on air. The show might be coasting along on autopilot at the moment but in comparison to anything else it still sparkles.
Also, on repeated viewings it is funnier. TBBT has always had great repeat viewing strength (like all great comedy) but I didn't "get" a lot of season 5 until I'd watched it twice - my wife thought so as well. Does that mean the scripts are not as well written? It certainly isn't the acting, which is as good as ever.
So overall, not as good as past series, but still funny and worth viewing. 8/10