Having never watched the cartoon series, I'm basing this series as a standalone.
Overall, it is a solid. Not great, but most certainly undeserving of the shallow critique "professional" reviewers give it.
With only 6 episodes, it most definitely seems rushed. Given that, it was an impressive feat to give just about every single important character depth and development. The plot has some intriguing twists that definitely keeps someone watching, though it should be detestable that the first season ends in basically a cliffhanger with too many unanswered questions.
The most severe, and probably most glaring issue of this series is the world-building. Are the only staff in Alfea really only three people? Especially when the show draws literal comparisons within the script to Harry Potter, Alfea hardly seems magical.
One other important gripe is how all the fairies become buddy buddy is like... not done well at all. Sky and Bloom being in the same scene together 90% of the time makes me want to tear off my balls. Zero chemistry between the two. Bloom feels a bit tropey, but tropes aren't inherently bad.
Barring these issues, this series can still provide a compelling story with multiple characters with depth.
Characters: 4/5
Plot: 4/5
Acting and script: 5/5
World-building and setting: 1/5 (Is there no such thing as Asian fairies? This is contemporary fantasy...)
Not the best thing you'll ever see, but in comparison to a number of other fantasies, it's rather good.