There is an epic barge ride up the Congo and Oubangui river to the remote river port town of Impfondo (and onwards to Bangui in CAR).
Hwy 1 to Pointe-Noire has long been in such a bad state as to be almost impassable. Today upgrading work is ongoing and the journey time is dropping. Still, even with the improvements it still takes at least a day by bus. Hwy 2 north to Ouesso, however, is paved and in mostly good condition to just north of Makoua. Beyond here there are still some horribly rough spots, but reconstruction work is underway.
A few proper buses now run to the north, but it's still mostly bush taxis and lorries. Europcar offers expensive car and 4WD hire, but it's easier and about half the price to just charter a taxi with driver for travelling around Brazzaville. Or for cross-country travels you can go to Brazzaville's Marché Total to haggle with truck drivers parked on Ave Matsoua; the best price we found was CFA100,000 per day. The Hotel Hippocampe can also provide an excellent car and driver for a reasonable (for Congo at any rate) price.