I did the Chengdu – London return at the start of this year too. Good flight times (leave Chengdu about midday and London at about 5pm if I remember correctly..). The flight was full on the way to London but virtually empty on the way back which was great for spreading out and having a row to yourself (plus the crew were a pretty cool bunch). Not sure how much it cost exactly as it was part of a return trip to Argentina but would be happy flying them again.
Last year came back from Australia flying Melbourne – Chengdu with Sichuan Airlines. Managed to get put up to business class which was spacious and relaxed (compared to a crowded economy). Flight was smooth and service was fine (especially after they realised they could speak Chinese with me instead of English), but the IFE was rubbish with one straight-to-DVD movie being the only English one, and the rest being Chinese/Russian/Korean/magicians (and I was told I couldn’t use my iPad). Food was okay, and the bed was okay although not fully flat, not that me as an economy traveler cares too much..