Well, I think timetravel is way over used in Trek to the point where it seriously seems easier to travel in time, than travel from point a to point b. A whole series based on it and an episode that doesn't make very much sense? Meh... especially given the innate corruptness of arresting someone for "crimes you are going to commit." Relativity wasn't even that good of an episode really... though I found it funny that the time cops hated Janeway... though somehow I don't think the writers were going for that.
While Trials and Tribbleations is a good, fun episode.... making something like that the norm would lose it's novelty really quick.