I managed to install Generations without any problems, took about 30mins to actually update my game though, since I never have and never will do automatic updates so I have quite a few patches to install when it comes time for me to add an expansion or stuff pack.
I have noticed I've been getting Error 12 on my legacy game more often, this was before I installed Generations as well as after. So I think I might have to research and try out the fixes and workarounds, it's not usually a hassle, I don't mind replaying a lost day. It usually happens when I try to save after changing too much, buying and selling, building, editing any sim in CAS along with everything that happens in the regular day. I'm kinda worried about my new project because of it, since I think I read somewhere that the bigger the house and the more stuff you have, the more likely you are to encounter an Error 12 message. However I have been planning to build a totally new house for this legacy family which includes double the amount of space they currently have, three stories and a basement (their current house is one level).
I couldn't put a treehouse on the Neverends current lot, kept telling me it was on a slope for some strange reason (the ground was totally flat). However I added all of the other new playground items.
On the first day the nerdier of the three girls (Dakota) woke up on the wrong side of the bed, and started having a mood swing, much to my surprise. She rolled some interesting wishes, including skipping school, being mean to her mother and getting into a fight with another sim, all of which I fulfilled. She also, of her own accord, booby trapped the shower after getting dressed, resulting in this.....
I think after her tempter tantrums and trouble making Summer and Shayne might send Dakota to boarding school to straighten her out a bit, I'm leaning towards the Snobby Prep School.
So far it's pretty fun, all the new interactions and things for the younger family members to get into make playing them more exciting....I'm finding I tend to let Summer and Shayne do their own thing on free will even more now.