I used this line yesterday over the four northern stops - Dalston, Haggerston, Hoxton, and Shoreditch High St, as part of my work, and it is amazing what you can see from the train line that high up.
I also used it this morning to commute from FH to Dalston, and my journey was reduced from over an hour and a quarter to just under 50 minutes! I too can't wait till 23rd when it opens up all the way past Sydenham.
Very quiet though (in terms of peopl) - I was sure that more people would get off at NCG to use the new line. maybe it'll be a slow burner.
several people did appear to be using it to get to Canada water, to change to the jubilee line (instead of going via LB) which makes sense, and at Whitechapel, and Shoreditch almost all of the other people had left.
My only criticism is that at least one of the stations (SHS I think) is classed as Zone 1 - I was under the impression that they would all either be zone 2+ or at the lowest a zone1/zone2 borderline station. What this means is that if you travel on the entire line, you have to go through zone 1, and so can't claim the reduced fair for avoiding zone 1 (ie a zone 2 and 3 only travel card!) I thought the idea of London Overground was that you could travel 'round' London, without going 'into' the centre.
I guess it's just another way of making us pay more money.