I have to concur The Executor should be a big surprise left for ESB (the PT takes away too many of those already)...It was a wow moment to see those enormous ships from ANH dwarfed by the HUUUUUGE ship in the next one.

It continues with the idea of escalation.

Really the Death Star in ROTJ is a bit of a let down, to make the point that nothing can stop the Emperor he should have replaced it either with something obviously even bigger and more powerful or with more of the bloody things (two at least).

It turns fighting the Empire into fighting a Galactic Hydra (blow up one huge superweapon and two grow in their place).