If you'd like to add some things that are a bit more under the hood and technical ...
Mali-400 GPU
AnandTech described the GPU performance of the Mali-400 as "staggering". To quote the review ...
"Despite huge disadvantages in geometry performance the Mali-400 does extremely well in the Egypt test, outpacing most of its competitors by a factor of 2. Only the iPad 2 is faster but that's to be expected based on the raw horsepower of its GPU. Given current workloads, ARM's Mali-400 is clearly the fastest GPU available on a smartphone today."
CDMA in the 800mhz ESMR Band
Only a few Sprint phones have this capability, including the HTC EVO 3D released in June, and now the Epic 4G Touch. Unfortunately (depending on how much you care about such things) it was left out on the Motorola Photon. Here is a description of what it means from an article on Phone Scoop:
Sprint currently uses iDEN technology in the 800 MHz ESMR band, but plans to migrate to CDMA technology in that band. Phones will need to specifically support CDMA in the ESMR band in order to take advantage of that part of the network.
The benefits won't be anything terribly obvious to consumers. It will simply mean more capacity on Sprint's CDMA network, to support more customers and more usage. Over time, it may give Sprint a competitive advantage that allows them to offer cheaper 3G data plans, for example. It also means that things will simply continue running smoothly. As Sprint gains customers and as those customers use more data, they risk running out of capacity. That would lead to degraded service, including dropped calls and slower 3G data speeds. This move simply helps them avoid that scenario.
There is also the benefit of increased building penetration. That's not a huge problem for most Sprint customers, but if it's a problem for you, you may find you get better service with one of these new phones, once Sprint deploys this network upgrade in your area.
5ghz WLAN (WiFi) Support - Dual Band
Here it is described, again from AnandTech's review:
"The SGS2 has both 2.4 and 5 GHz WiFi connectivity courtesy of Broadcom?s newest combo chip, the BCM4330. That puts SGS2 in an incredibly small list of smartphones that include 5 GHz WLAN support, which is critical going forwards as the 2.4 GHz ISM band gets even more crowded."