Hard to add anything to the great comment by rsjsouza.
For me the main limitations are:
* Weak FFT - slow, low number of points, poor UI, text same colour as trace so hard to read. I still find it useful.
* ADC chips running hot. I intend to add heatsinks as well, just haven't got around to it...
Not sure I'd bother reading that other thread though, like many of the Rigol DS4k threads it escalates rapidly
Worth noting that the strongest critic in that thread doesn't own one and only used one briefly.
When I got mine it was a no-brainer as there was nothing else available in 4 channels with the bandwidth and features for the price (via hackability)
There are more options now so it's worth having a good look around.