I have the same problem with the LEDs I bought. The cause seems to be that the LEDs are mounted too close to the front of the package. Other people have reported better results, and their LEDs seem to have more diffusing plastic in front of the LED dice.
I got some improvement by putting a piece of acrylic rod, with sanded ends, in front of the LED, held in place with a chunk of heat-shrink. But I'm still not really happy with it.
Bottom line seems to be "Caveat emptor": get samples before you buy a lot, and make sure you buy from a vendor who will deliver exactly the same as the samples.
A better diffuser might help, too. Perhaps one of those domes they used to put over incandescent panel lights?