I had a great stay at the Sheraton Park Lane this past october as an SPG platinum using points for 2 nights..Got upgraded to a full suite with a view of the park.
We weren't in the hotel too often, so can't comment on the services...for the limited interaction we had, they were fine.
The only complain is that the rooms are a bit dated and the furnitures has a 'tired' look and feel to it...But that is also what gives it a classic look and feel I guess...
The elevators were also small and slow, so during busy mornings, it took awhile to go down..
Best aspect of the hotel is the location....We were able to walk to Buckingham Palace and Big Ben....also walked to the theatre district, and shopping around the Oxford street.....
Drawback of the location is the lack of choices for dinner.....but its close to the Tube that you can get to anywhere..