Kgalagdi does not have elephants or rhinos, but it is top notch for predators. It takes a little more planning than Kruger, but not that much more. You will most likely need to do some, most, or maybe all of your own cooking for example. The consistent advise is while you do not need 4wd, an SUV type vehicle, or similar light truck is generally recommended.
Our last 2 trips to South Africa have included both Kgalagdi and Kruger. We picked up the rental car (a 2wd SUV) in Johannesbrg and drove between parks. On both trips we included a couple of smaller parks as well.
While not really "like" Kruger, some of the smaller parks in South Africa offer a very nice experience. Mapungubwe and Mokala in my experience are both nice places for a short visit while traveling between the larger parks. Marakele is one that I hope to visit on our next trip.
I have looked for places that offer a similar value to the South African National Parks, and have not found it. I conside value to include the cost of getting there, the cost of being there, what we will get to see and do, and a few less tangible characteristics. Self driving in the parks is pretty hard to beat.