We've cruised before numerous times with Celebrity and have been on Summit before. It's really gone downhill. The ship is old and tired, there is rust everywhere, many of the areas need repair and repainting. All the niceties for a premium cruise are gone. Batheoom and Spa changing amenities are just basic now. No cotton buds, cotton wool, body lotion etc. Hard selling on the first day was overwhelming and on everything, upgrade your package, but speciality restaurants etc. The food in the main dining room is great but choice is really abysmal, Buffet is sadly a better option.
Entertainment not great and its very sparse in timings. The musicians do just 45 minutes and there's huge periods in the evening where there's no music to listen to anywhere on the ship!!!
I have to say though that the room/bar/wait staff are FABULOUS.