Our experience in order: Boarding at Southampton, if arriving by car you line up, when called forward you move around to an "unloading area" where your luggage is taken away by porters. Then drive to the nearby car park, walk to the terminal and go through the normal check in process. Simple, no fuss, from car to ship in 20 mins!
The boat, Celbrity Eclipse. Spotless, contemporary, plenty to do and see. Cabins well appointed, staff really friendly with a good morning or good afternoon round every corner. General "feel" of the ship was brilliant, never felt crowded although at times in the evening had trouble finding a seat in any of the lower deck bars. Food was first class, all hot, tasty and well presented by chatty waiters. The cafe food was also well presented with a mindblowing choice of what to eat. Entertianment was good, accepting that different acts are not everyones cup of tea so this is really your choice, we liked it though.
The itinery, which included Gib, Southern France, Italy, 3 ports if include Sardinia, Cadiz, Lisbon and Vigo was spot on, with ports intermixed with days at sea allowing time to relax, catch up on the sun tan etc.
Was there a downside, well yes. Why is it that even when everything is explained clearly in the documentation, and there are 45 seats on a bus with only 30 passengers that some people have to moan! and I am sorry to say mostly the older generation over 60's, it made us cringe! Otherwise BRILLIANT