Hoping the things listed below will get better for V6...
Solid tools produces bad results and the excuse is that nurbs can't do that.
Section tools was going somewhere but stopped.
Clipping planes almost there but can't snap to clipped geometry.
The interface with tabs not total customization compared to other programs.
Drafting can't rely on it for larger projects though I use it, needs a parametric link to 3d objects.
Printing, been waiting for tiling since V3, I know it's on the horizon.
Shelling, and offsetting of solids and surfs only recently been added thank you but still buggy on some simple shapes where it should work.
Meshing just keeps going in circles and still no way to store export settings.
Other modeling paradigms. Drop the elitist nurbs moniker and embrace mesh modeling and voxel modeling along with nurbs. It's time to add these kind of modeling paradigms to Rhino to make Rhino a giant fearsome beast.
Some convolution of the interface that has settings buried deep within sub menus and drop down menus and too many mouse clicks to get to. Hopefully some weeding here.
Block editor needs a major overhaul it's modal you can't open it and still work in Rhino. A spread sheet control on another tab in the BM so we can really organize and use blocks that exports directly to excel and can stream to excel as well.
It's easy for me to list shortcomings, I know McNeel is a hard working firm and very receptive and helpful.
So here's the good...
Killer cplane use and mplanes attached to objects is awesome.
Great rendering support of many programs.
Awesome mesh repair tools and wow my molds are flawless from Rhino. Also my cutter cuts patterns and pounces are printed right out of Rhino.
Many ways to interact with rhino from Macros, GH, Python, Vbscript,.net, c#,c++
Killer polyhedra plugin
Great curve and line drawing ability, along with editing, if only other programs were this good.
Awesome snaps that actually work compared to other programs
Pretty good interface to make your own customizations up to a point.
No macintosh support
Many many great plugins at affordable prices
Great support for large files and dense models that would choke other programs.
Great openGl and viewports with many modes to use to visualize your models in realtime along with fantastic analysis tools.
Robust not much crashing.
Very straight forward 2d and 3d modeling compared to other programs where it takes many more mouse clicks to do modeling operations. This is Rhino's strength
Awesome transform tools
Great little helper things like library tab, notes, ability to work in any units.
Nice rendering tools right out of the box and good mapping and unwrapping of materials
Awesome amount for import and export file formats
Tech support is the best in the industry
Great great price.
I could go on about the good but that's preaching to the choir.