Yes, I have played all the games (other than the spinoffs). The original FO was developed by Interplay, whereas the sequel was handed over to Black Isle Studios (a subsidiary of the publisher). Some of those BIS bigwigs developed FO:NV at Obsidian (the FO2 influence is obvious). I never enjoyed FO2 because I felt like it went contrary to many of the design principles behind the original game (such as the game's fine balance of darkness and humor, which the sequel tipped towards the latter. FO1 had many moments where I would laugh, then think.). I enjoyed FO:NV, but not as a Fallout game, just as the good RPG that it is.
I was happy with FO3 because it was more clearly influenced by the original game (in terms of setting, as it fell flat as an RPG), and I was hopeful that with FO4 they would follow suit and attempt to perfect it . Apparently, they have taken a very different approach. That's fine, as I can judge the game on its own merits, but I still can't help but feel disappointed.
I hadn't thought of that, but I think it would be a GOOD thing if the actors had very different styles, as it would help counter some of the criticisms the voiced protagonists have received. Two different styles means twice the chance that you can find a voice suitable for a particular build you want to play.