I can vouch for the mice. I was there in April and again in May and saw one in the lobby and two in the now-closed Chambers Club.

As someone has already mentioned, the Barlow rooms are being renovated. They started on the sixth floor and are working their way down. I stayed in a recently renovated room (weeks old) on the fourth floor.

To complement the London Marriott lounge discussion, the JW Marriott has a decent lounge. The food offerings are limited, but the staff is friendly, and the building was recently renovated.