A good deck summons fast, and still has room for devastating spells and traps. Most of the best cards in the game work with Blackwings. This means that they can draw more cards faster than most archetypes, use the advantages of the graveyard, summon quickly with high attack splashable monsters and Synchro Monsters with exclusive and powerful abilities.
When a professional reads a card they see certain kinds of effects, the usability of these effects determine how good something is. These effects are those that relate to Special Summoning, the Graveyard, Synchro, Darkness, Light, and Drawing. The more of this, the better. The type of a monster also helps find compatibility with old school cards that help that type significantly (as in, nobody predicted that Icarus Attack could support such a well off series of cards).
If you use Royal Oppression or Red Dragon Archfiend/Assault Mode they will be severely weakened.