Grass is good for raster processing. If they ever got away from having to set your own regions and import every dataset, it'd be way better. It's pretty clunky and hard to use and some tools simply don't work well or at all so its always trial and error. However, it is free and has many tools that work really well. I like it overall but it leaves a lot to be desired for usability and algorithm stability. I've had tools fail and fill up an entire hard drive with garbage. The flip side is that it can be fast and return good results if you get lucky.
Has a ton of tools. The GUI is ugly and unfriendly, but it's perfect when used as a QGIS integration.
wake up! almost everything in gis is here, and free, and working... what do you want?