I biked out there this afternoon to visit REI – the whole place was very busy at 2:30 pm on a weekday.
I have to say that in spite of the fact that it's absurdly impractical to get there without taking a car, the Rock Row site itself is unusually well designed for bike and pedestrian access, with calm access roads and nice landscaping, and a nice wide path that connects Brighton Ave. to the side of the quarry next to Market Basket.
All of the surrounding roadways, though, are an ugly, chaotic mess, and absolutely murderous for getting foot traffic to or from the site.
Driving through that area is also pretty unpleasant, unless you enjoy long waits at red lights (although it seems like lots of drivers out there do, since so many of them are gunning their engines to maximize their time waiting at the next one).
The City of Westbrook needs to do some serious pedestrian safety improvements on Main Street and Larrabee Road if they're actually on board with the developers' vision for a walkable mixed-use retail center. It's absolutely absurd that Larrabee Road is five lanes wide – it's as though the city is trying to make more drivers crash into each other.