Any character recast takes time to get used to. I remember way back in the early 2000s, I couldn't quite get used to Eric's Bert and Grover, David's Cookie, and I thought Matt's Big Bird sounded similar to earlier Caroll performances when Big Bird was more of a yokel than a kid.
That was then, but now, I don't think nothing of it really; it's like Oscarfan said, it's all about the character and the personality.
Not to mention, even when Jim was alive, there were various performer and voice changes within the characters, and not just on SST. Mildred had been voiced by Richard, Dave, and Frank; Nigel used to be a Jim character before John Lovelady started doing him; Janice was originated by Fran before Richard played her; and let's not forget Miss Piggy didn't start out as the regular, breakthrough character she became, and went through different performers, including Richard, before Frank took her fulltime.
That was then, but now, I don't think nothing of it really; it's like Oscarfan said, it's all about the character and the personality.
Not to mention, even when Jim was alive, there were various performer and voice changes within the characters, and not just on SST. Mildred had been voiced by Richard, Dave, and Frank; Nigel used to be a Jim character before John Lovelady started doing him; Janice was originated by Fran before Richard played her; and let's not forget Miss Piggy didn't start out as the regular, breakthrough character she became, and went through different performers, including Richard, before Frank took her fulltime.