Ah... so your looking at a whole package move.
Then a lot depends upon many factors, what are you prepared to budget in creating new libraries, training for your team (an untrained user is a poorly informed user and cannot use the tool correctly), do you need to be able to import Altium files into CADSTAR or are you prepared to draw a line in the sand and only use it for future projects? What sort of technology are you currently designing and looking for in your package?
i.e. are you using high speed, multi BGA, DDR etc or are you just making relatively simple, low speed interfaces etc?
IMO if you simply download the express\demo version of V15 and then try to use it you will likely be put off just like I would when sat in front of Altium or any other package
Simplified - You create symbols, components and then parts for your library (throw away the provided one), setup schematic templates, add parts to the schematic, connect them up, setup route widths to control the track width etc then transfer to PCB, you setup the layer structure you want, create a board outline (manually or DXF\IDF in) place components, transfer into the router and then route your tracks, flood fill copper shapes for your planes etc. transfer back to the PCB editor, finish the board off, produce manufacturing files (Gerber or ODB++).
I suspect this process is very similar for other packages - its just how you do it that is slightly different, the result is the same - a Green board thingy. (other colours are available)