Besides the fact that she's an awesome looking Angel for collection purposes, Deathpact Angel isn't the most impressive card. For 6 mana, only getting a 1/1 token when she dies with an ability to essentially to recast Deathpact Angel from the graveyard doesn’t feel like a mythic rare, honestly. While you’re not technically recasting her, it essentially costs you the same. She was honestly a very good Limited card during the Return to Ravnica block.
She's also not bad in Commander, especially if you pop her into play off with Kaalia of the Vast's effect to put an Angel, Demon, or Dragon into play when attacking. Some Commander players have played her alongside Teysa, Orzhov Scion for some synergy with her effect, since both the Angel and her token are both white and black.
Her artwork is pretty awesome, but I wouldn’t play her perhaps ever outside of a Kaalia or Teysa deck. She's a bulk mythic rare at this point, seemingly only printed at that rarity to not become overpowered in the Limited environment.