Well I loved it.
The fact that little Miss spoiled brat face like a slapped arse heavily pregnant came over to Gemma trying to be all nice to her after treating her with utter contempt, on every single occasion previously, said a lot. Then telling her they were finally moving away completely (which was exactly what Gemma wanted), was a triumphant moment, while Gemma said not a word in reply, cool, calm and collected. We also learned from that conversation that Simon was allowed no contact whatsoever with wife and son - not even to call. When Kate said her parents were 'glad too' it was because they also wanted her and him gone, not because they were helping her.
Meanwhile Gemma got everything she wanted. Simon and Kate gone from her world, her life intact, neighbours, colleagues, the house, the money, her son ... and clearly given the way it ended with her rushing into doctor mode - her career. She outwitted and out manoeuvred them all.
Meanwhile he climbs into the old car (plot device to illustrate how skint they are) with Kate and unborn child. It wasn't a case of driving off into the sunset at all. They were going because they had no alternative, there is nothing there for them any longer. His look was wistful and full of regret, not a happy smile.
The fact that they ended up together doesn't mean he's somehow won. Two selfish entitled weak unpleasant characters who deserve each other. Gemma was the winner all round on every level. The only thing she 'lost' was a weak, pathetic, hopeless with money/business, cheating, lying husband. Everything else in her life remained intact and in many respects better.
I thought it was fine ending, and have thoroughly enjoyed the whole series from start to finish.