I don't use my car often and it's small so I only go to this Shell once a month or less. The price is generally lower than at other locations - consider that it's right across from the Galleria.
My main reason for going here is that I get air miles(yeah I fall for that) in addition to the savings at the pump. You can't pay-at-the-pump because this isn't one of those fancy service stations but the guys inside are nice and the place looks clean. There's a diy car wash too incase you're riding dirty.
In the summer if the price of gas is really low expect it to be a total clusterf***. I'm talking cars backed out into the street, blocking traffic, loads of honking. I once made the mistake of joining this frenzy but quickly regretted it. I'd rather pay an extra .20c elsewhere, those people might be packing heat.