I just went to the Skytrax reviews for BA, and the "scathing review" of SYD-LHR turns out to be the most recent review of BA, posted today (2/14) and therefore currently at the very top of page 1.
So, if I'm looking for other opinions, I scroll down, and then go to the next few pages. And looking at the first ten reviews of WT+, they give the following marks out of 10 (starting with that "scathing" one) -
1, 6, 10, 3, 6, 5, 10, 8, 10, 9 - That's an average of 6.7/10. Not bad.
If you eliminate the lowest and highest score (the 1 and a 10), you get an average of 7/10.
So I'd say, based on my tiny piece of research, having never flown WT+, nor BA long haul for a very long time, and of course not working for BA, I'd say 6.7-7/10 is fairly good.
Of course I'd then go to the other airlines that offer a premium economy cabin for the route I plan to take and compare the reviews and scores for them.
And no, sorry OP, I haven't flown it so can't contribute an experience.