[mikeash]

Blue Origin's rocket is returning from a bit above 300,000ft and roughly zero speed. Falcon 9's first stage is returning from a similar altitude but at mach 6.

That adds a lot of difficulty just in terms of getting rid of that speed without destroying your hardware. Plus you need to aim from a lot farther away. The Falcon 9 includes hypersonic grid fins to steer towards the landing site, for example. (Failure of these due to running out of hydraulic fluid is what caused the first landing attempt crash.)

Just getting to that state requires a lot more of the rocket as well. If getting to that altitude is the equivalent of going mach 3, then the Falcon 9 first stage is putting in the equivalent of mach 9, so that's 9x more delta-v, which means the rocket needs to carry vastly more fuel and be vastly lighter.

All in all, the Falcon 9-R is trying to optimize for two things at once, which is always difficult. Landing a rocket vertically is not that difficult. Landing a rocket vertically while having that exact same rocket also be useful as the first stage of an orbital launcher is way harder. It's a bit like building a flying car: there are good cars, and good airplanes, but trying to build a machine that's good at both is far more difficult. Hopefully SpaceX's effort works out better than flying cars have.