I am a LONG TIME fan of this show.
I don't think it ever went "bad".
However, I will say this...the period when Rory "chose" Emily and went to Europe with her and all that was uncharacteristic of the character of Rory. Lorelai going out with Luke FINALLY (I'm a L/L fan) after ALL THAT TIME...then just to be disregarded because Luke "suddenly has a daughter" was complete idiocy. I did like his daughter's character AND the actress who played her. But would the real Luke truly just give up Lorelai just because of that fact and shut her out? I don't believe so. Yeah, they get together in the end, but that blip in time still peeves me off.
That said, I have all 7 seasons on DVD and they are all wonderful. It's one of my top 10 shows of all time. Love it!