Well, I'm a Poser to DS convert.  I jumped to DS around verson 3 because I got tired of Poser's clunky interface.  DS was far faster and it had a modern interface, so I switched.  So it's not like I switched to DS4 just for Genesis or anything.  I doubt I would, either.

But to answer your question, I'm tempted to move from Gen4 to Genesis (and am slowly doing so) for several reasons:

1. Autofit.  It gives me better results than WW or any of the other conversion software ever did, with far less work, in a much shorter time.  This is huge for me.  It turns my separate gen3 and gen4 libraries into one big Genesis library, with all the new stuff for Genesis on top.

(Side note: when are these conversion programs going to learn about feet?  The way they mash shoes around the feet makes me think they're approaching the problem the wrong way.  IMO it doesn't matter if footwear really fits the feet; what matters is that I can hide the feet on the figure they're conformed to and pose it and have it look good.  They should give up on making the footwear fit well.  And it's about time someone figured out how to do the "fall off" so heels aren't mangled - can I get an "amen" here?)

2. More morphs.  I love me some morphs.  The more the better.  Again, it's like having all of V4's morphs, plus I get Genesis' morphs, too.

3. Better bends.  I've heard that Genesis handles extreme bends better than Gen4.  I have yet to test this, but if so it's a selling point.

But there are cons.  I expect they'll be smoothed out over time, but as it stands now:

1. As someone else mentioned, there's no good way to handle what morphs are loaded with the figure.  I've recently delved into making my own "forks" of Genesis but this is not straightforward.

2. Morph sorting sucks in DS4.  Flat-out sucks.  The Property Editor is a half-arsed klunker barely worth of the "beta" label.  They actually charge people for this lemon!  I don't know if it's going to be fixed for DS 4.5, but right now it's a real nightmare.  It makes molasses look fast and crashes on a regular basis (it literally takes like 5 minutes to get it to load a figure on my computer, which isn't cutting edge by any means, but it's not a dinosaur, either; 8g of RAM and a 3ghz dual-core processor)  This is pretty lame and I think it has to do with DAZ's stupid attitude toward morphs.  They seem to think what is a stock feature in Poser (drag and drop, create your own folders, etc.) should be a black art open only to content creators.  They're wrong, and need to stop letting Poser kick their butts on this issue.  This is one of the only things that ever sends me back to Poser - organizing morph dials for Gen3 & 4 figures.

Really, DAZ needs to create a simple app that will let people manage morphs.  They're very good on most things, and I'm frankly kinda shocked how cool some of their innovations have been over the last couple of years, but they've got their heads you-know-where on this morph organization thing.

They also need to overhaul the content library; make it run as its own process so we can browse the library while DS is wasting my time saving/loading, and give it "virtual" folders and organization like Advanced Library, but that's for another thread.