Though I generally like the early 1970s seasons best, IMHO "Agenda for Murder" is maybe the very best of the latter-day episodes and it's certainly on par with many 1970s episodes. So no, I don't think you'll be disillusioned :)
Of the newer ones, I also liked Columbo Cries Wolf because of the ingenious plot and Murder: A Self-Portrait because of Patrick Bachau's great performance and the terrific musical score. Some of the later movies made Columbo's humor too cutesy.