First, just because you buy an iPad for drawing or sketching, it doesn't mean you can't play games and watch movies with it, plus, if you have access, you can get online and use it as you would at home.
Second, I can relate my experiences with my first generation iPad. I am using it as my primary sketch tool for use on field trips and on the road. It saves not having to lug around paper, pencils, markers, erasers and all that other gear I used to lug all over the country. I don't use it for final, finished work. I never used my sketch pads for that purpose, anyway. But the iPad is easy to pack and is useful for a LOT of other things including note taking, GPS weather info, playing my music, online radio stations, and a ton of other things that saves me having to pack other gear.
The question remaining is thinking about whether or not it even HAS any cons. Well, it IS rather expensive when compared to a two or three dollar sketch pad. But it also replaced what could add up to hundreds of dollars of other gear, not to mention carrying all that additional weight. I'm ready to upgrade to a newer iPad, mainly because I need the pressure sensitivity of the newer screen. With that, I'm sure I'll finally have the final tool I need to really replace my traditional sketching tools.
I also like the built in camera features of the newer iPads, but I'd like to see more examples of its performance. It WOULD be nice not to have to carry around twenty pounds of SLR, lenses, video equipment and a tripod. And i love the idea of a viewfinder and playback screen that size. But for my needs, high quality images are a paramount need. I'm ready to upgrade my cameras, but I'll check out the capabilities of the iPad 2, (about. Hundred bucks cheaper) and the iPad 3.
My favorite drawing apps include Sketchbook Pro, iCharcoalpad, and ArtAppFree for simple line sketching. I have quite a few other apps, mostly free ones tha I will be playing with as I have time.
Your question about whether it's worth can only be answered by you. Are you getting what you need with your existing tools? Can you get what you need with additional apps? Will getting new gear fulfill your needs and is it worth the expense to get that?
I have a question for you. What is it about the zgenius pad that you can't take it anywhere?