For me, first going to the OP was not love at first sight. I was put off by the weirdly small bar area (most people sit at tables, or a counter near the windows with several pier-type things give it more surface area) and smallness of the place. But now I love it. This is the go-to bar if you just want to hang out and shoot the breeze with your friends over relatively cheap drinks and free (!) popcorn. I usually get mixed drinks because I'm not a huge beer fan, and while they aren't cheap (I think $5.50-$6.50 is the norm), they do usually come in a pint glass, which means they're a good value compared to many bars in Burlington. There are, however, lots of beers and tap (the Vermont faves like Switchback along with the standard fare like PBR) and good daily specials.
Only pitfalls of the OP: slightly skeevy "regulars", oddly placed pool table (be prepared to be accidentally poked with a stick while waiting for your drink) and questionable tacos. But then again, if you're drunk enough to crave an OP taco, you probably won't remember it, so you'll be okay.