I love FP, but they jumped the shark when they had Will's mother marry Lisa's father. Will and Lisa were such a great couple and it felt like the writers hit the panic button because they wanted to keep the dynamic of the series intact.
That might be the biggest mistake they made. And watching part one of the series finale, it was really depressing to see how much Will was struggling to get something going on while everyone else started moving on without him.
He could have just moved back to Philly. That was the original series finale anyway until popular demand brought the show back. Why did he stay in California for school if the Banks were no longer there?