I could get lost here.
The gallery layout is uninspired; it's made to be open, so you can wander from room to room to room, and it's rather like being in a rectangular beehive. If it were full of filing cabinets I would think of it as great modern art and then leave.
There's a nice little courtyard, but it's really not what the gallery was made for.
What it is here for is this: there are hundreds of gallons' worth of paint on the canvasses here. (Certainly the paintings aren't the only attraction). You will not be able to spend a single day at the National Gallery. Not a single week, even, if you want to see everything. The art is beautiful and reflects a very broad spectrum of interests - classical to almost-modern. The hours are great, and you can't beat the price. (Just don't destroy anything you arent ready to replace.)