I’ve been following the Philly Church Project for a while because they have reviewed some of my favorite places. I’m not too much in favor of reviewing churches like they were restaurants but it is what it is. From the review:
What to say about St. Mark? Well, I like the place. If you can survive a somewhat bland exterior (aside from a really neat angel-flanked inscription on the front), you’re treated to a great medieval interior. Gothic, columned and non-cruciform, it’s stone through and through except for the ceiling, and it’s kept nice and dark so it’s a great throwback to the wrath-of-God era. Probably the dysentery era, too, but the less we say about that the better.
Overall they give it a pretty good rating, which you can see here.