Essentially, you get 7 power for 6 mana,. If you sacrifice the tokens immediately for mana, you get 5 power for 4 mana, which is pretty solid. It's a really good card in Limited to tap down opposing chump blockers, leaving you able to swing for big damage.
Is it Constructed worthy? It didn't appear so when it was first released. The occasional Standard Eldrazi ramp deck found room for it, but it didn't look like a breakout sort of card. Typically, though, creatures that bring along two dorks with them end up seeing some sort of Constructed play. Pia and Kiran Nalaar, for instance, is a perfect example of this sort of card. With how the newer Eldrazi have built-in ways to ramp with their Scion tokens, dropping this guy on even turn 4 isn’t impossible.
Finally, at Pro Tour Oath of the Gatewatch, Jiachen Tao ran 4 copies of the Drowner of Hope in his winning Blue/Red Eldrazi deck. In Modern, Eye of Ugin and Eldrazi Temple were available to accelerate big Eldrazi creatures onto the battlefield early in the game. Because of this, Drowner of Hope's power level in Modern became a lot higher than it could ever be in Standard. It was possible to drop it on turn 3 and turn the Scions into extra mana or tap down opposing blockers to prevent chump-blocks.
Not only has it proven its worth in Modern, but Drowner of Hope has a nice enter the battlefield ability useful in Commander. It can be abused through flicker effects in decks like Brago, King Eternal. He’s easily played ahead of the mana curve and a solid creature. Drowner of Hope is definitely above-average as far as intro pack rares go.