Well,, its been a while since I saw the first two series - hence no posts - but this continuation did largely engage me, although I felt that the penultimate episode was somewhat overfilled in terms of plot - and this, was an element in the whole series (and often can be with series if they continue for more than 1 or 2 series) where one felt the writers were adding more and more different elements to maintain interest and dramatic impetus.
In the first, and involving and often second, series of multi-part shows, a major part of the engagement, for me is a gradual exploration of how the main characters come to terms with themselves and their situation, be it with a supernatural element or not and their personal journey is often more engaging than subsequent plot lines when they are at ease with themselves and where they are., The dramatic often internal conflict has been resolved. To keep the momentum, writers often, it seems, add new groups/factors/situations to maintain interest. This certainly happened with True Blood, to give just one example which, for me, definitely went off the boil once Sooki entered fairyland. For me the best aspect initially was the apparently ‘ordinary’ setting and how the characters mixed their two lives - that with their special powers and hat with the ‘ordinary’ people in whose world they live. And I know that a, if mot the, major reason why Spiderman (and, to an extent, the Batman Trilogy) are favourites; the central characters are much more than their supernatural/superpowered personae and their ordinary human conflict, internal and external, are the most engaging aspects of the story. This was the case with the first Reeve Superman - his coming to terms with who and what he was, was what made it so powerful and engaging.
This has been the case with Sabrina certainly and so perhaps it is a good thing that the next series (4) is the final one. In addition, the time-warping plot which allowed the viewer (and Sabrina) to have their cake and eat it was dramatically and emotionally unsatisfactory. Was nothing learnt from Back to the Future (which was actually referenced in the situation)? Sorry if this seems gnomically enigmatic, but do not want to drop spoilers; if you have seen the series you will know what I mean!
Anyway, we will see with the final series.