It's not bad but on the nights that AF has two flights (5/wk, soon to be every day) it is very very full.
Seats are comfortable, drinks and snacks are decent.
There is a shower, not sure about internet though.

I was told that in 2 months or so the current KLM and AF lounges will close at JNB and move to a brand new location at terminal level (no more stairs/escalators) in the new terminal.
It will be a larger, joint lounge, operated by AF and they are looking into accomodating other Skyteam airlines like DL.
Long overdue and looking forward to it as I take the Europe-South Africa route at least five times per year.