Well, before starting this message, I'd like to apologize. When reading again my previous message I realised it sounded really harsh. It sure wasn't my intention, and I'm sorry about that.
Now, I understand that the saves will be compatible (which is already ALOT better than what I had read is some review...), but if the whole game has been changed, and if maintaining compatibility meant not applying some of the changes, basically, I feel cheated. I find it disgruntling that having been suportive very early means that I will either miss new content / changes or start over.
I do understand the technical reasons and all, but I'm still pretty disapointed. Since there is nothing to do about it, more informations would allow me to chose whether to start over or to skip the changes.
Now, if such information doesn't exist yet, my best choice is most likely to wait until such feedback exists.
Anyway, thanks for your answer.
