I don't think the droid x is trying to be an "iphone killer" but rather a successful android based phone for both moto and verizon.
With that said, the droid x certainly has some advantages over the iphone. I think a lot of the knocks of it being too big are a bit unfounded. I test drove an evo and found that it was not ungainly large at all (and be inference the droid x not being to big). The large display made videos, web and typing an order of magnitude better.
It seems the battery life is much better then the EVO as well - at least based on this review
engadget
Personally, if you like the iPhone UI, or you want a gaming device instead of a phone, then yeah the iPhone is a better choice. What I like about the android platform is choice, I have plenty of apps, I can load on custom ROMs, I can make all sorts of customizations to the phone, i.e., custom TXT notifications. No overseer dictating what is appropriate to see/read/use on the phone.
I'm not knocking the iPhone and there are plenty of advantages to the walled garden approach. One size does not fit all, and so the droid x is a great phone on a different carrier that fits a need that the iPhone doesn't.