I agree some plot points of the later seasons could have been better (e.g. why would >!it be necessary to, even if she'd eventually get them back/be able to recover them, erase all of Holly's memories of Eureka instead of just those of the Astraeus mission!<) but imho it's better than you think and not the worst decline of that kind of show (looking at you last two seasons of The Librarians, at least Eureka managed to (as much as it could with the Weird Time Shit) remain internally consistent)