Just completed a 5 night stay. Location is good as far as centrality is concerned, but Piccadilly is a bit like NYC 5th Avenue. We found the lounge to be surprisingly good, especially by US standards. Even though the breakfast offerings were all cold (I think there may have been a toaster), the food was well-prepared and tasty. The espresso/cappuccino/latte machine that ground all the beans to order was a nice touch.
In terms of Plat upgrades, not so much. Our room was on the top floor (8th?) with a view to the northeast, but nothing great. Clothing storage was a bit problematic. No drawers in the room whatsoever, just 3 cubbies in the closet which meant I had to get down on my hands and knees to find my stuff every morning. Hotels in Europe don't let you use a hairdryer in the bathroom, just in the room itself which is where the only dryer-appropriate outlet was and seriously insufficient lighting for this task. The rest of the room was fine. The bathroom had a nice window and towel warmer, but very little horizontal space for toiletries, etc. Staff was very pleasant.
Would I stay here again? Likely not. I think I'd try the Sheraton Park Lane over LMP.