Happy to echo what everyone above has said and thanks for the recommendations – some notes from my visit to the *A lounges:

TK: Terrible – can skip without a worry in the world.
BR: Surprisingly good food although the buffet is not perhaps the most splashy – even relatively ok pizza. Nice ice cream.
TG (new lounge in the D concourse): Pretty nice atmosphere and decor, although perhaps a bit too big. Was nicer to sit in the very end where it was quiet. Both Häagen-Dazs and Ben&Jerry's ice cream.
SQ: Smaller lounge with the best decor of all the lounges, feels cozy. Good buffet of food, incl. Singaporean chicken rice, fresh coconuts and Häagen-Dazs ice cream. Champagne, albeit quite a cheap one, is a nice addition for a J level lounge.

All in all, for previously a oneworld-only guy, this was a nice eye-opener with regard to the standards of lounges in *A.