The writing is lazy and the dialogue is especially atrocious. It's sounds like they took a bunch of kids from our world playing a D&D campaign.
There's no sense of space in this world. Members split off and go decidely different directions only to pop out of a secret tunnel next to each other. Oneinute they're in a barren wasteland being stalked and then they're running through lucious green grass.
The cameo in the last episode was absolutely pointless and so hamfisted that it really spoiled the moment.
Lastly, whoever decided on the soundtrack needs to be fired. YOU HAD A PERFECTLY GOOD SCORE TO ADAPT AND WORK WITH! MODERN POP COVERS DO NOT FIT THIS WORLD!