This place automatically gets bonus points because it's close to where I work. In all fairness though, I give them a solid 4.
1) Friendly staff - everyone here is so nice. They recognize you when you come in, they say hi, ask how you're doing. Try getting that at Starbucks.
2) Reasonable prices - enough said. $1.97 for a large coffee. Sold.
3) Baked goods are crazy good. Do yourself a favor and get a blueberry scone or a white chocolate raspberry scone and ask them to heat it up for a few seconds. I'm talking life-changing flavor. It's like eating a muffin top with that little crustiness to it, but the WHOLE THING IS LIKE THAT. And then they put some icing on it, you know, for good measure. If you want to be happy while simultaneously hating yourself for not eating healthier, this is the ticket.
Those are the top three reasons why I like Erin's. The sandwiches I've had so far have been decent, but not quite at the level of the baked goods section.