The first mile or so is fairly uneventful. Once a rapid with a boof left appears, the action begins. Only two rapids are definitely class IV, but there is a lot of III+. With the number of strong III's it warrants an easy IV rating at moderate levels. At high levels (>1.5'?), it is a definite IV with some push.
A particularly fun rapid can be called 'the bed'. The bed begins with some big pillows, eddies through the mattress, then you fall off the 5' high endboard. A slide about halfway down often has good surfing. The good rapids come in two parts separated by a flatter section.
The second part has several fun rapids, and two of particular note. One is a triple slot: The left slot is now finally do-able with a slide to the right edge since the tree that partially blocked it for years shifted in the big flood of spring '03. The hardest rapid is towards the end and involves going right to left to avoid a hole and catch a leaky eddy on the left. Watch out if you catch the eddy low, a slot may suck you in. At high water, the hole can take you down and put you through the slot whether you like it or not. It has a semi-distinct horizon line with a narrow line against a rock on the right and a hole upstream of an eddy on the left. A scout is often in order here.
As of summer 2003, there is a lot of wood in Blackoak. None of it requires a walk at 2", but higher levels may require some portages. Most dangerous in the second drop of the bed, to the left of the pillows. There are two bad logs here. Alternate routes exist to the right but a scout may be required.