I liked the original series for its novel approach to the world of superheroes. A youngster, accidentally given alien technology to shape-shift, imbuing him with various powers, enjoys his role with the guidance of his grandfather and cousin, allowing the audience to learn about the initial alien characters, and slowly gain knowledge and access to a few new characters hidden in the Omnitrix.
The new series starts a few years later, as, apparently, the eponymous youngster is disconnected from the device, without explanation, and his cousin has gained advanced knowledge of her mystical capabilities. But, the grandfather has gone missing, and Ben is forced to don the Omnitrix, once again, to search for Grandpa Max. But, the device changes on his arm, giving him an entirely new set of creatures from which to save the day. He and Gwen are joined by their one-time foe, Kevin. On the plus side, the Omnitrix seems to give Ben more knowledge and control over the characters, as well as more time to use those characters. The same is true of Gwen's advanced powers.
On the down side, the three are without adult supervision, which I had found to be something of a relief, if not comfort, compared to kiddie shows which had no parental or adult supervision (e.g., "Kids Next Door", et al.), and even those having such supervision, but of whom were clueless dolts (e.g., "Fairly Oddparents", et al.). Furthermore, instead of allowing Ben to give the new creatures fanciful names, he spouts their name or species after he changes into them, which, in my mind, at least, somehow takes something away from Ben, and, inevitably, us, as well. Also, the foes seem to be an inexhaustible supply from one source who, of course, want to take over the Earth; as with the Daleks from the "Dr Who" series, and the Borg from the "Star Trek" series, this is going to get real old, real fast.
While it's nice to see the kids develop into more self-assured personalities, the new series is wanting, from missing background details - - which I'm sure will be revealed in excrutiatingly slow detail - - to the lack of both believable characters and novel plots. This is no longer a new series, or even merely an extension of the old one; after just three shows, it has become a sad parody of itself, with, seemingly, nowhere to go, but down.
Truly a shame, and a loss of an otherwise good series.