For some reason, in among their repeats of episodes from season 3 to 5 the BBC the other evening showed Episode 2 from Series 1: "I Never Met the Dead Man". It was interesting to see how things have changed since then. Back then, the characters seemed to be drawn using much bolder black lines to delineate them. Chris's nose seemed different. Meg's hair was longer and darker than it is now.
With the change of actress, not surprisingly Meg sounded completely different. But Lois also sounded quite a bit different from what she does today. Even Peter and Chris sounded a bit "off". Only Stewie and Brian's voices seemed not to have noticeably changed over the years.