This place is more like a 3.5, but I'd rather round up than round down. The ramen here is great! I ordered the miso ramen and requested that they make it spicy. The broth was rich and flavorful and the chashu was perfectly cooked (my 3 slices were so tender they barely stood up to the chopstick).
The noodles were definitely not fresh, but that would have been asking for a bit too much for a small shop in Pittsburgh. Still, Zen's is the best ramen in this city.
They also give you a 10% discount if you pay in cash.