THREE REASONS Island Creek Oyster Bar has been an early hit: It has a big space that’s fun to be in, a restaurateur who knows how to make a lot of people happy even when the place is packed, and a chef who knows both how to get good fish and how to best show off its flavor. Oh, and having a co-owner who runs a thriving oyster farm helps, too.

Luckily, Island Creek had a master strategist: co-owner Garrett Harker, who turned Eastern Standard, on the other side of the Hotel Commonwealth, into a crowded hit, with food and décor straight from a French brasserie playbook. Much of what makes the restaurant work is his talent for pleasing both locals and the stream of Fenway-going crowds. He seems to be doing that at Island Creek, too. As with Eastern Standard, the new restaurant’s bar scene is an integral part of the fun, and with bar manager Jackson Cannon now running the cocktail program at both restaurants, people are coming to Island Creek just for his drinks. And the place looks great — casual, inviting, and not at all scary. The brightened space takes oysters as its theme: wire crates filled with oyster shells along the walls, oyster-gray banquettes, and silvery wood-plank screens that slide across the windows.

As for the food, it’s aimed squarely at seafood fans, with absolutely fresh fish and shellfish. That’s guaranteed by the expertise of its other co-owners: chef Jeremy Sewall, who, not incidentally, opened Great Bay and has been helping Harker at Eastern Standard while keeping his own Brookline restaurant, Lineage, busy; and Skip Bennett, the Duxbury oyster farmer who made Island Creek Oysters a prestige brand in Boston and beyond. The restaurant gets not just its pick of perfect oysters but, through Bennett and Sewall’s friends, excellent New England fish and seafood, too. It’s sparkling and, with only a few exceptions, cooked to exactly the right degree — a remarkable feat given the 175 seats and the high rate of turnover.

The way to sample both Sewall and Island Creek at their finest is to start with oysters and stick with time-tested family recipes. As for the rest, well, the fish is seldom anything other than first-rate. But the dishes themselves are uneven. Specials are particularly hit-and-miss — though one was the best dish I had in four dinners.