What makes a Digimon card good? 

Good video

I'd argue Goddramon X is a good card it just doesn't have adequate support 🤷‍♂

GoldramonX is a weird comparison because it's a pretty decent card. It helped revive 3 great dragons as a playable (albeit still meh) deck. It's effects are all good but the good cards that could support it are all seccon cards that don't want it. Perhaps the biggest reason it's a poor comparison is it's not really meant as the core level 6 of a deck. it's meant to be used much like fighter mode is. I do agree that interrupting how your opponent plays is immensely strong though. That being said Dragon mode is an exceptional card. It gives an effect no other deck really has that allows it to totally counter aces.