They definitely need to update the AI in the game - but the engine isn't showing it's age to much. The game looks absolutely stunning - I am running it 1080p Ultra Settings and get steady 60fps most of the time on a GTX970. I think the draw distance could be extended a little further across the board for both object detail and shadows - but overall it looks great and runs very smooth.
Getting rid of the towers and letting me unlock the map at my own pace is my favourite refinement for the series - and completely renewed my interest in it as well. Other than playing FC4 on PS4 for 2 or 3 hours and FC3 for maybe 15 hours total I completely skipped on the series. I do have Blood Dragon installed - but I never made it through the tutorial on that one.
I don't think I will likely go back and finish those games because of FC5 - but I am now looking forward to seeing where they take it next.
Oh - and I might still get Primal. The concept always interested me - but I still haven't bought it. I may get it next time it is on sale if I have some spare steam money.