I like these threads, I have been to a lot of different services too, maybe we can start our own ship of fools site :)
I wonder if you will try Catholic or Orthodox? I've enjoyed Orthodox services because they are very different in style to the Western services, I think you would find it interesting.
I haven't had a good time at the pentecostal services I've been to either, I did prefer the vineyard church and charismatic Anglican church I've visited, I wanted to explore that aspect of Christianity and found they did it with less of the baggage of pentecostals, I.e. Without prosperity gospel theology and over promising on healings, though I don't know how much variation there is between churches. Interestingly Vineyard theology had the biggest influence on the Alpha course (more so than standard Anglicanism) which has done a lot for Church of England survival, and they had a lot of influence on the Archbishop Justin Welby, so maybe you would enjoy that from a sociology perspective. I think I would also be interested in your reflections on 'contemporary' worship (I don't think you would enjoy it but could be wrong? I expect this style will become the norm in British Christianity in a few decades)
Personally I would like to explore some anabaptist (I.e. Mennonite) churches but the last one seems to have closed in London a few years ago. I learned of a Lutheran church in London I might visit soon, I understand they are struggling to survive over here too, but much like the mennonites have never been very prominent in Britain anyway.
My worst experience was with the Korean Shincheonji - their dishonesty and treatment of their followers and potential followers was quite incredible, they are growing rapidly but it remains to be seen how they will survive their leader's death - he has promised he will live forever and he is 86 now.