Welcome to the board, Rathswid!!!
Reviews are meant to be taken with a BIG grain of salt!
I rarely trust them unless I have followed the reviews of a particular reviewer for a long enough time to understand how their and my tastes in games are similar or different.
You'll find a wealth of information on this board and lots of friendly help to answer your questions.
One of the great things about this game is the flexibility of character development - there are so many possibilities and it is near impossible to make a mistake! My general rule of thumb as to when to change class is as follows: For magic users learning a new school of magic - I won't change them until they have learned all the spells I want them to learn (there are some spells which are not worth learning at all). You can, however, change a Wizard to a Warlock earlier than that implies with no problems, the wizard will continue to learn the spells he/she was learning. Fighter types I generally will switch earlier than magic users. There are advantages to changing a warrior into a barbarian or paladin at a lower level than you might consider changing those learning magic spells.
The best advice any of us can give you is SAVE SAVE SAVE - multiple saves. Try something, if you don't like it, reload the save prior to the changes. This is a very flexible game and lots of fun!
Do keep us posted on how your game is going once you finally get it!!
Wyv