Or even Unity over X10. That's more or less where I'm headed since Unity is a very user-friendly. Unity's licensing is even better than Unreal's; 100% free and no royalty fees no matter how much you make (you only have to buy the pro version for $1500...after you've made your first $100,000).
But back on topic. The only real reason to use X10 over either of those two I guess would be for super fast prototyping or light level design to get layouts right. And maybe as a way to make games with literally no prior experience (Unity and Unreal are a little more advanced). But outside of that, I'm afraid I can't see too much use for it either, at least as far as making real games goes. I don't know about Unreal but in Unity, importing assets is literally drag and drop, in X10 it can be quite the hassle (as you well know
). I've already imported one of my custom guns, hands and all and used it in-game. Just need to modify the script so it uses my animations and voila, custom pistol (It already shoots, has glowing lights, particles that spawn from the impact point and has ironsights. Could easily add a flashlight if I wanted to go L4D style).
I guess it comes down to what you want to do. If you just want to mess around for a little while and make something then yeah, go X10. If you're serious about making an real games though, X10's not good enough, for me at least. Although if all you're going to do with X10 is mess around for a little bit, you'd be better off with X9 since X10 was supposed to be the one for more serious developers.
Unity Engine 2.6 is now available for FREE
http://www.unity3d.com