Watched it with my son. It was OK-ish, I thought. Mind you, having paid for Prime just to see GT, I can see why Amazon wanted the old TG team and why GT was the most watched Prime show - we flicked through the rest of their offerings and it is real dross.
Despite a lot of talk in reviews about it showing the benefit of the big budget, I struggled to see it. Perhaps they blew it all on the opening sequence, which was the best bit. Despite the title of Grand Tour, which made me hope for more of what was good in the TG specials, there was little advantage taken of the location; the super cars were in Portugal, their track bit was in the UK somewhere downmarket and derelict. The Ebola gags were, IMHO, regretable. The overweight American driver was not a good feature.
The banter sections seemed forced and did not flow in that natural, almost unscripted looking way they managed on TG at its best. Let's hope subsequent episodes will get better.
Having said that, I thought their last few series of TG were already in decline. Notably the substandard India special. Nothing lasts forever suppose.