There are flaws with the show, but I wouldn't say they are as bad as people are making them out to be.
I find it really surprising that people are picking the acting apart, because it's more or less the same cast from the later sequels. Cera, Ducky and Petrie are all from LBT V and later, and Littlefoot is from LBT XIII. If I'm being honest, I thought the acting was fine. We were lucky that the producers even bothered to grab voice actors from the sequels to do this show. It's normal tradition for a TV show based off of a movie to have completely different voice actors for a lot of the characters, while there are some exceptions to this. Now if we are talking about the acting of the side characterss (Ali, Hyp, Rhett, etc...) then I can see where the acting is unsettling. But looking at the main seven, I didn't really see any problems with the acting.
While I agree that some of the songs are not the best, the repetitiveness I'm a little forgiving towards. It's not surprising that a lot of the songs are reused because it is a TV series, so it's more cost efficient to just use different versions of the same song. Does it make the songs tolerable? Not all of them. However, I can understand why they would be repetitive.
I found the plots acceptable for TV episodes. Of course, some were better than others, but I didn't find them terrible. Sure they were not as expansive as the plots for the movies, but they are suitable enough to fulfill the requirements for a TV show. As for the plot holes, they are only so jarring because we are already long time fans of LBT. The target audience of the show, younger kids, are not going to be as familiar with the history of the franchise and its characters, so they won't notice any of the plot holes that we do. Yes it's not cool to us, but at the same time lets remember who the show was supposed to be geared towards.
The animation isn't the best, but it's not terrible. Sure Universal and Amberlin have created animated shows before, but there was a nine year gap between this and its previous show (I think Pinky, Elmira and the Brain was 1998), so I think it's only natural that the animation is not the best. Yes, they've been doing all of the sequels, but at the same time the sequels had a bigger budget than the TV series.
Is it a perfect series? Of course not. But does it really deserve the harsh criticisms some of us are giving it? I don't think so. It's not the best, but it could have been a lot worse.