The Club (galleries) lounges at Heathrow are actually pretty good. Compared to any US airline lounge (which domestic passengers have to pay to go into) they are definitely two steps above.
The T5B lounge is great because its less busy than the T5A lounge, it has the same service and food and beverage.
Also I'd say, better than many of the European airline business lounges, which can be quite lacklustre.