Inside the Parks, there tends to be a good excellent infrastructure of roads, some of which are tarred, others gravel. Signposts at road junctions help to make the driving experience easy and enjoyable. Drivers must remain on the roads at all times, and are NOT allowed to drive off-road or get out of their vehicles, except at designated viewing points.
Driving times within the Parks are also restricted to daylight hours only, so you can only enter the Park just after sunrise, and you must be off the Park roads by sunset.
It is not always necessary to go to the expense of hiring a 4x4 hire car, unless you are travelling during one of the rainy seasons, in which case a 4x4 would be useful to splash through puddles without worrying about flooding your engine out.
However, a 2WD vehicle with a high clearance might be worth the investment, as it gives you a few extra inches over the people in their VW Polos to see over bushes to search for the wildlife!