Rotterdam is a much newer city than most of the other big hubs in NL. It was bombed a fair amount during WW2 so the buildings and infrastructure is more modern than Amsterdam, Haarlem etc. Den Haag is also somewhat more modern but mostly because of its political concentration I assume.
Rotterdam has 2 very distinct reputations depending on who you speak to. People I know who live there love it but a lot of people more north (i.e. Amsterdam and surrounds) say that its rougher and more gritty.
That said NL is so small that as long as you are still in Noord or Zuid Holland (provinces), working in Rotterdam doesnt mean you need to live in Rotterdam if it doesnt tickle your fancy. Leiden to Rotterdam is 30mins station to station, Utrecht to Rotterdam is 35-45mins. Den Haag to Rotterdam only 30mins. I work in Amsterdam and have at least 4 colleagues that live in Rotterdam and commute here everyday.
Also, since most Dutch companies will subsidize 50%-100% of your work travel expenses, you needn't worry too much about cost of train fare etc if live a bit further away. You can use
www.9292.nl to get an idea of distance to the office and
www.funda.nl for an idea of property prices in and around stations/work place etc.
I've been living here for a few years now and am pretty pleased with the decision all round. As long as you can deal with the weather, it's a pretty easy country to live and integrate in. As a SA citizen you will need to do a 'inburgeringscursus' which is basic language proficiency and an exam on how the state systems work (I have an EU passport and didnt do it so I dont have much more info to offer there I'm afraid).
There is a trend here to offer people temp or fixed term contracts because there is some legislation that you can keep someone on temp/fixed contract for up to 3 years before you are made permanent so be aware of that for contract negotiations. Also, as an expat if you are brought over for the job specifically you should qualify for the 30% tax ruling which will see you paying 30% tax for 8 or 10 years so long as you stay with the same employer (there are some caveats, so investigate that). It really makes a difference on your take home and is a nice bonus for anyone who qualifies!
If you want any other specific info, feel free to PM. Hope the above helps