I'm surprised they're still going, though it has gone far from its glory days (or so I think) back in the mid-90's to the early 00's.
There used to be a large one near where I lived, near Baclaran LRT station, it is an anchor tenant of one of the old "tiangge-style" malls in the area. It has three floors, which delighted child me back then. I spent lots of time looking (reading!) books, browsing stuff, and just going around.
Then there's the large five-storey one in Avenida (midway between Carriedo LRT station and the intersection with Recto). I used to pass the time there, reading books, while waiting for my eyeglasses to be done (in one of the optical shops in the general vicinity).
Now, the branch near the Baclaran LRT station has long been gone, and the one at Avenida is a shadow of its former self (the other "side" has already been closed). I haven't been to their large Cubao branch (next to Gateway, meron pa ba?) for a long time but I used to spend some time there too, just browsing books, a bit of downtime in the middle of my commute.
It is also kinda depressing to see how it's gone more and more into being a stationery shop than a bookstore. I guess they have to do it to survive, but it's still sad.