Ok, I'm not from Philly, and I don't claim to know a "good cheesesteak" by Philly standards, but I do know good food - and this is it.
When you pull into the parking lot at the Houston Texadelphia, you'll know you're there because every car in the parking lot has a UT or Texas A&M sticker on it. Don't worry, it's a good thing.
The restaurant itself is probably one of the last things you'd expect in the Galleria area of Houston - but it's a good, cheap, out-of-the-way place (as is Mama's next door).
The Houston Texadelphia is slightly different from the "original" one in Austin. When you walk up, you come between two wooden buildings - to your left is (what looks to me like) a "private party" or overflow room. It's got some wooden tables and TVs and on nice days, a breeze blowing through it. To your right is an enclosed porch-type area with lots of wooden picnic tables and more TVs - usually a little bit more populated, since it is closer to the kitchen. Keep walking - straight ahead is an outdoors congregating area with a basketball hoop and not much else - looks like a good place to hang out during a BIG game if Texadelphia gets too packed. From there, immediately to your right is the main room. It's got all the sports/beer paraphenelia, more TVs, big screen TVs, and the kitchen/bar area. This is the only part that's air-conditioned too (a great place to be in August in Houston).
Grab a wooden chair and sit down at a table. Grab one of the yellow paper menus on your table (located next to the wooden six-pack case holding salt/pepper/napkins/straws on your table). Order yourself up a cold longneck and start reading the menu. I've heard that some of their other food is also very good - but you've got to try the cheesesteak sandwich. Available with either chicken or beef (I like the beef) and with a wide variety of sauces (ranch, spicy mustard(what they (& I) recommend), BBQ sauce, etc). All that comes on the delicious bread is the meat and onions (grilled together - so be sure to tell them to take them out if you don't want them!). The sandwich comes with chips and their homemade salsa. The chips & queso is a good appetizer.
Basically, Texadelphia is just a sports bar with a fun atmosphere and really good food.