A large amount of the stuff in the store, free stuff and the more exotic textures for clothing and hair only work in Poser4. So if you really want to get "close" to realism, you don't have a choice. Poser 3 is really a waste of time in comparison. Though in itself it's a good package. There are so many variables that it's difficult to detail them all. I seem to recall someone did a feature list when Poser4 was released but I don't recall where that would be. However suffice to say that P4 is half again what P3 used to be. Probably the biggest difference is in the mesh quality (P4 figures are somewhat better than P3) and in conforming clothing. Which means clothing that parents to the main figure, and moves with it when that character animates or poses. Transparencies are a secondary bonus to this, but for realistic hair and clothing variations it's a whole new toy and there are endless variations you can use it with. For instance someone is constructing a zombie character using the Poser skeleton and default P4 male, using transmaps to "break" the skin for the skeleton to show through. Things like that just aren't possible in P3. On top of this is the ability to use jpg for maps rather than just tif, am improved software engine, better rendering (though not by much) and a fairly large stock of default figures, clothing and "characters" (pre morphed P4 male and female figures with skin tone and face morphs to characterise them) It also comes with a couple robots, the usual animal stock and a largish though mostly useless (IMO) set of poses. What else is there... erm, off the top of my head, slightly better variation and control over the lights, a refined though similar animation engine, better walk paths with slightly easier way of setting them up. More control and variation for texturing and the facility to import/export to a larger group of applications. Someone else can fill in the blanks, but that's what springs to mind to start with. Poser 4 isn't so much an upgrade to Poser 3 as a whole different way of doing things. Even with the few quirks that it has, you won't be disappointed.