I stayed several times at the Cavalieri before moving to Rome and in my opinion, after visiting a few hundreds of 5 stars hotels, I still consider the Cavalieri one of the best hotel in Europe, expecially if we compare it to other european Hiltons or WA. Now I usually attend events at the Cavalieri (if you are a wine enthusiast at the hotel twice a months there are top class wine tastings managed by the Italian Association of Masters of Wine) and for this reason I have the occasion to visit the hotel at least once a month.
In november I also stayed at Conrads in Bangkok, Singapore, Hong Kong and Tokyo (all of these stays at the executive floors or in suites) and after this experience I still consider the Cavalieri much better than these hotels.

Many of the posters seems to forgot the rebranding of the hotel from Hilton to WA in 2008 and the changes related to the rebranding. The Imperial Lounge is one of the best lounges I have ever visited. Obviously to access the lounge you have to book and pay for the Imperial Floors. When the hotel was an Hilton this was the only lounge and Diamonds and Golds had free access. Now lounge access is not a published benefit in any WA hotel, nor the free breakfast. The so called Colosseo Lounge is an added benefit for golds and diamonds: it seems poor, I agree, but consider it as a benefit like the free breakfast. I never received a free breakfast in any WA hotel I stayed, apart the Cavalieri. Per T&C the hotel has no obligation to offer such benefits.
It has no sense to compare a former Hilton hotel during its golden age to a rebranded WA.