Just like anything else, it's easy once you learn it, but can be confusing compared to Milkshape for example, which has an interface similar to a lot of other applications. Download the demo first, try making a few things, and watch the gamespace video tutorials.
If you find it easy, buy it, but don't take my word for it; everyone's different.
Also, after you download the demo, they'll email you deals and sales time to time (usually around holidays), which are often much less than the posted price on the site. For example, a few months ago, Truespace 5.2 was being offered for $85 I think, which is less than half of what its being sold for now. And gamespace, which is normally $300, is not only being offered right now for $200, but they will also include DarkMatter and a robot model with it!
http://www.caligari.com/gamespace/web_special200603.asp
So definetly download the demo first and try it out