While the meals are worth their full price even during the non buy one get one nights of the week, they cannot be beat during the special. They have a really varied menu with something for everyone unlike some restaurants which give you just a few things to choose from on specials like this.
The family style salad they serve at the beginning of the meal is delicious and there's always plenty for however many people are at the table. The service is VERY friendly despite the fact that they're always busy they always seem to be on top of things like drink refills and letting you know how your order's doing.
No matter what you order, it's definitely going to be good. Everything I've had (or tasted from my friends plates) had been delicious and we always like to try new things instead of always getting the same thing which is a good sign because it means that you're afraid to stray from something you're used to and comfortable with.
Portabello is definitely worth a visit, or a few a month actually... the menu is great, the service is great and the food is great. You throw in the special and you cannot beat it!