The series is different from the darker and more serious series Alien Force and Ultimate Alien. It is more light hearted, more comical, the art is changed radically and it lost some characters. Despite all of that I think it is a good addition to the Ben 10 franchise.
Personally I feel Omniverse is closer to the original series than the last 2 were. That has both positives and negatives. Ben being unable to control the Omnitrix transformations has been a problem reintroduced since the third season of Alien Force and happened on and off in Ulimate Alien series, but in Omniverse it is like Ben mistransforms 8 out of 10 times, which becoms painful after seeing how much he mastered the previous Omnitrixes in the previous two series. It is a weakness to have the mistransformations be so high, since it implies that Ben's mastery of the Omnitrix has regressed to his 10 year old self. A bad move, because Ben should be learning more control of it at this point.
What the Omniverse does right is the rotation of the alien heroes. It is hands down much better than Ultimate Alien was. We are ten episodes in and we have seen aliens from the original series, AF, UA, and Omniverse's own orginal aliens. I have been impressed with how they are avoiding just using their own creations most of the time. A problem I had with the last two series was despite having so many aliens the writers clearly favored their own aliens and AF and UA series. One complaint peoplehad was Fasttrack was used repeatedly and XLR8 wasn't used in UA ever.
Ditching Gwen and Kevin is a move I think is a bold move, after watching 98 episodes of Ben, Gwen, and Kevin team (that is both AF and UA episodes combined)fans may have a problem with losing those 2. That team has been going longer than the original Ben, Max, and Gwen team in the original. The creators claim it was CN that imposed that rule on them. However, I do not think it is a horrible move. AF changed the game by making Max a supporting character and made Kevin a villain in original on a team with Ben and Gwen and even gave him a romance with Gwen that was out of nowhere for fans of the original. What was worse as that it took years before the writers explained why Kevin's character changed so radically in between the original and AF.After a few years it turned that change actually worked. Rook being introduced may not be a bad move yet. He is sterotypical alien paterner who knows nothing about Earth culture, but I think it works right now. It keeps him from being the same as Kevin and Gwen in terms of personality and power sets. The character can be a welcomed addition and the change in format may more acceptable or less annoying as time goes on.
I can't comment much on the storyline yet, because it is still forming.This hunter guy with a dog that has a Omntrix device could be either really bad or really good. At this point I do like that guy.
The animation is bad to me. I won't lie. I prefer if they used the animation from the original series or Generator Rex like they used in the Crossover movie (which blew AF/UA animation away too).
All in all the series has its share of problems and has room for improvement, but it has it shares of positives as well. For the demograph it is going to keep kids interested. I would say it is average right now. If it progresses more it will develop darker storylines like the Ben 10 series that came before it.