I would say yes, essentially Flashback, but with different terms and effects. I imagine there will be creatures with aftermath instants, or even cards that are one color and the aftermath will be a different color. I must say I am impressed and excited. This seems way cooler than the stuff that happened in Kaladesh.
You can't just cast spells from your graveyard so RAW it seems you would need something to trigger it. I'm thinking that wouldn't be a keyword-worthy ability so you'll probably just be able to do it whenever.
Okay... Dusk is pretty good. Always on the lookout for decent wrath effects. Dawn, though... can anyone think of a use for this outside of commander? I struggle to think of any deck that wants to load their hand with a bunch of cheap creatures... and that has 5 mana to spend on it.
Ugh I hate the design of these cards..