Me, before PGSM: Sailor Moon is about the milennium-spanning Miracle Romance between Usagi and Mamoru. Usagi and her friends transform into Sailor Senshi to protect the world and fight evil!
Me, after PGSM: Sailor Moon is about how much it sucks to be reborn and still have to deal with the consequences of your past life. There's a one-sided love triangle between Usagi, Mamoru and Ami, a tragic love between Rei and Minako, and Makoto is just doing her best while sweeping her own issues under the rug, damn it!