I agree with Aaren. Mercury was made when Celebrity was still being creative with ships. Compare her spaces with Century, different foyer, dining room, Rendezvous, nightclub, theater, almost all major public areas are different. What's similar? Layout. The Mercury is daring and creative, nice combo of grand and intimate areas. Compared with Galaxy only the stairwells are similar, otherwise, both are their own ships though they are almost identical from the exterior.
Quality of German ships is better than French made Millennium. And Millennium ships, same foyers, same dining rooms, same Rendezvous, same Covas, Celebrity creativity only shown in the different specialty restaurants. Otherwise, public areas follow the dull carbon copy route with different colors and patterns of other lines. Some areas, like the thellasotherapy solarium area and photo areas and even the shopping areas are much too similar to RCI ships.
Mercury, for me, is the last real Celebrity ship.