it depends what you're printing and what you want.

s3d has some really cool features. The multiple process approach is great. You can print different infill and resolutions into a single model. so for a big model that just needs fast 0.3mm bulk printing for the majority and then needs 0.2 or 0.1 for a small detailed area. s3d is the ONLY slicer that will let you do that.
It slices very very fast.

It prints under and over hangs much better than most slicers, so - yes you do get better quality prints.

The only bugbear for me is the infill: it's piss weak. It simply won't print a solid infill. Even on the lowest setting it only prints alternate layers. So things snap laterally realy really easily.

At the moment I use s3d for most things. But for anything that requires strength I have to use makerware.
Which is pretty good, but nowhere near as good for over & under hangs.

Any complex model goes through s3d 'cos it slices about 20x faster than makerware.

I like it, it's not finished yet. Still needs dual extrusion sorting and infill. But if you want to manipulate layer and infill within a single model - it's the only slicer that will let you.

Is it worth the money, for me - yes. Or at least it will be when they sort out the multiple extrusion and infill.