In most sci-fi shows, time travel is usually just a one-off deal that never has any lasting repercussions. But it forms the centerpiece of "Eureka Season 4.0," in which a single jaunt back in time causes sweeping changes for the citizens of Eureka -- it sounds like a cheap way of shaking things up, but the focus on what time travel has changed is pretty interesting.

Carter (Colin Ferguson) is out jogging on Founder's Day when he suddenly goes back in time to the year 1947, along with Allison (Salli Richardson-Whitfield), Jo (Erica Cerra), Henry (Joe Morton) and Fargo (Neil Grayston). With the assistance of scientist Trevor Grant (James Callis), and are able to get back to present-day Eureka.

But... some things have changed. Jo is the security chief of Global Dynamics and never dated Zane, Kevin is not autistic, Andy the robot is Carter's new deputy, Henry is married to a woman he doesn't know, and Fargo is now the director of Global Dynamics. Oh yes, and Grant has come forward in time with them.

As they try to adjust to this new timeline, they have to deal with mysterious power surges, a zombie-style rage infection, a super-oxygen infestation, random teleportation (from 1947!), stalkerish A.I.s, people turning into stone statues, and hallucinations of people from the past. And Dr. Grant starts discovering that the future isn't all it's cracked up to be.

I was starting to lose faith in "Eureka" after the disappointing Season 3.5, which was basically a bunch of standalone episodes. And while "time travel ripples" sounds like a cheap way of shaking things up, it actually works quite well here -- the writers spend the entire season exploring the repercussions of time travel.

It sounds kind of grim, but there are some fun moments keeping it light -- particularly a cute Wall-E-esque robot, or Carter throwing the despised Fargo a ravening horde. The one real disappointment is the Eureka crossover -- it's not really BAD, but Claudia Donovan's visit is kinda anticlimactic because... she doesn't do anything except ogle the machinery and make out with Fargo.

Colin Ferguson continues to be charmingly down-to-earth, even as Carter gets enmeshed in a very tense love triangle with Grant and Allison. Also fun: the writers take some clever pokes at Carter's role in the show ("Hello, I'm Sheriff Carter! I'm going to save the day with my everyman logic! Ha ha ha!").

But all the characters get some solid development -- Jo is in turmoil over the loss of Zane, Allison becomes even more of a fierce mama bear now that her son is normal, and Henry starts falling in love with the wife he doesn't even know (although this happens a bit too fast). Oh, and Sheriff Andy is back as Deputy Andy, reciting bad poetry and suffering massive damage.

"Eureka Season 4.0" pumps some new life into this quirky sci-fi show, and rearranges some of the key players. Good stuff!

Many of the reviews state that this set is incomplete. It's not, but the title menu setup is terrible. When I first watched the set, I thought - like most reviewers - that there were only three episodes on the first disc (the first episode plus an extended version of the first episode, as well as episode two). From there, I moved on to the second disc, which contained only three episodes at first glance. So I watched those three after the first disc. Great? Not great. As it turns out, there were two more episodes on the first disc that you can access by either a) watching "Play All" rather than going to the episode index or b) finding the right arrow next to the first three episodes on the index that will take you to the remaining episodes on the disc. The arrow is not at all obvious against the photo image background of the episode index, as evidenced by the fact that most of us seem to have missed it. Now I'm forced to go back and watch the episodes out of order even though I know what happens in later episodes from Disc 2, which stinks. I would give the season a 4 or 5, but am rating the overall DVD a two for it's terrible design.

The first two seasons of Eureka were outstanding and original. Beginning in the third, however a sense of "been there done that" began to creep into each episode. Even the actors appeared to be losing interest. But happily, season 4 was just the infusion of freshness this series needed. Taking our main characters back in time, then sending them back to the present but in an alternate reality was stroke of genius, allowing the writers to reinvent many of the characters and their relationships, giving us some fresh takes on what was getting oh so stale. James Callis (aka Baltar from Battlestar Galactica) is a welcome addition to the cast this go around, as are the guest appearances of Wil Wheaton, the cross-over episode with Warehouse 13, and the return of sadly missed characters Nathan Stark, Beverly Barlowe, and Jim Taggart.

Now, if only they can get Jordan Hinson back into the regular cast . . . this show would be perfect again!