The best part about delve, and how powerful it might be, is that it doesnt need to abuse the graveyard to be good
Some details are locked up by Wizards, but theres enough info from the printing world and the MTG community to build a clear picture of whats going on under the art
Radha, Heart of Keld Radha, Heart of Keld really needs an Exploration-type effect in play to pop off, but with an extra land drop or two each turn, Radha can pull together an entire landfall strategy
Decks centered around Energy counters got some much-needed improvements when MTG Fallout was released, and now there are even more new toys to build around
My point is not that this is good because it is an instant rather, this is good because it is a swingy card that works with what blue is trying to do and has relatively low risk