You're absolutely right darlin', change does not occur overnight.
With that said, however; I'd hardly consider the six-year lapse between RE 2 and RE 4 to have occured 'overnight'. In this case, it is important to preach context. Leon was a rookie cop who went through hell and back in RE 2 which took place in 1998. In the next six or seven years, he trained in the Secret Service. Personally, I wouldn't expect him to be the same naive, rookie officer in RE 4. He's been hardened as an individual- not only through his training but from his experience in Raccoon City, and I believe it's an entirely valid development in his character. Extreme circumstances change people, I don't care who you are. Couple that with six-years, and there's no reason he should be the same individual we saw in RE 2.
Jill's personality consistancy- while obviously admirable to some, I don't particularly buy it, and that's probably why I've never taken to her as a character. She has probably been through alot worse than Leon, but there's not much development in her character on account of that. I don't find there is a whole lot of change between her character from the original and from RE 5, and I question the plausability of that.
So, in conclusion, whilst change certainly does not occur overnight, the producers of RE have certainly thrown a handful at all of the characters, and extreme circumstances in itself is enough to 'change' anyone. Yes, I understand that everyone handles things differently, but it's the characters who stay the exact same throughout the whole series that worry me, not the ones who change.
