The first two seasons were AWFUL, though they did pick up a lot after that. I mean, what a dumb idea to have the saucer section come off. Which stupid writer thought that that would be useful in space?
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Galaxy class starships are ships of exploration. With their extend stay in space, the crew of the ship were allowed to have their families to join them on their journey. The saucer section has the crew quarters in it. If for some reason the warp core or something else went critical, which was located on the lower part of the ship, they could separate the ship, saving lives in the process.
I prefer DS9 over TNG, but TNG improved after the third season.