I was a little disappointed with Arpa. I've had tapas plenty of times in a lot of different places (including Spain), so I knew what to expect - tapas = small plates = small portions. But at Arpa, it was just a little too easy to run up a big tab and leave hungry.
"Large" pitchers of sangria run $20 and are heavy on fruit, but light on wine. Baskets of bread are $3.50 each, and the create-your-own antipasto had larger servings of "accessories" than meats or cheeses.
All of the food was solid - the albondigas (lamb meatballs) were large and good and the bread wasn't bad - and it's cool to be able to relax outside and check the scenery. But when you spend $40-50/person, you wouldn't expect to leave feeling like you need to hit up Taco Bell on the way home.
I'm rooting for Arpa to find its niche, but Press (just down the street) wins the Trade Street tapas/small plates game hands down.