The local competition is pretty good right now. And it is truly local. Big Grove's initial impact will likely be to draw away from the others, not bring new customers into the market.
The Iowa City Big Grove absolutely
brought new customers to the market with the quality of the food and the overall experience. But they were the first place like that in town. I don't know how the brew pubs in Des Moines compare.
I will say that top to bottom I would pick Big Grove's beer selection over the likes of Confluence and Exile, as much as I like some of their individual beers.