I recently got a new iphone as well. Got mine off Craigslist, but I went for the 4, without the s. As far as I can tell, Siri is the main difference, as well as the better camera. I can live without both - don't need/wouldn't use Siri, and I have a DSLR for my 'serious' shots, and the 5mp of the iphone 4 is fine for those fun/casual quick pics a phone camera should be used for. The other major difference I guess is the processor, which in all fairness could lead to a more fluid and snappier day to day user experience, so that's valid...but I haven't noticed any real lag or freeze-ups with the 4 yet. All in all, it is worlds smoother than the Android phones I'm coming from.
Anyway, I'm just saying, considering how similar the 4 and the 4s are, I don't think you're exactly taking a HUGE loss by going with the original 4, it's a very close cousin.