I happen to quite like this series (thus far) as does my family and yet I can see why some people have a problem with it. First a bit of background: both my wife and I grew up with Scooby-Doo and our kids independently decided they liked the various instances of the show as well so, for good or bad, I've seen probably 99% of the Scooby oeuvre.
Certainly it should first be noted that this series is a "reboot" and not inherently placed in temporal or any other relationship to previous series. On the other hand, it is also often parodies what has come before. This has been done to some extent in the live action movies and the direct to video animated movies but in the present case, the basic world that the characters inhabit is more of an alternate reality. In the original series the chief fantastical element was that Scooby could talk; the present series supposes a town where monsters are big business and the kids get in trouble for SOLVING mysteries, for example. Structurally the show is more about action and character arcs with the mystery element largely on the second tier. In could be argued that the mysteries in Pup Named Scooby-Doo were a bit less obvious than some in S-D:MI (but the obviousness is also part of the parody, e.g., the gator episode).
As to the characters, Fred, Daphne and Velma all are pretty different from previous incarnations, as is Scooby who evidences far more social insight and complex dialog. Shaggy has never really varied much series to series and nothing much changes here (One has to go back to his very earliest existence to find him more adept and only mildly fearful). In general, these are not realistic or even particularly functional characters; great role models, they are not. If you are looking for that, the direct to video movies will be more your cup of tea. But if you are open to a different mythology with a more oddball yet somewhat more adult approach, you might find it a cool take.
I personally like the animation style and think the direction is on par with the upper echelon of current animated action shows. There's a bit of an irony in that the original Scooby-Doo was created in response to parental pressure against violence in animated shows of the 60's (e.g., Space Ghost, Jonny Quest) while this show is probably the most dark and violent Scooby yet. I guess things have come full circle.
In summary, I'd say give it a chance for a few episodes but if it isn't to your liking and you want something more classic/less dark/more realistic, I believe they are on a schedule of at least one new direct to video movie each year. Further, it appears we can probably count on new series productions for another 40+ years so you can always wait for the next one...
