Off the top of my head, I think I'm at just under 100 hours for DE, about 160 for 2 and ttg, and almost 300 combined for 3 and FR. I've loved all the games, but 3 and its dlc have grabbed me enough to want to 100% everything. Still haven't filled out soul hacker though.
On applications I've worked on, pretty much every time we've integrated SSO using oauth we've modified the entire login form to look the same. That means enter email, and we either send you to your provider login page or we show a password prompt after. Not a good reason in my opinion, but one that shows a similar UI regardless of login type.