Apple tends to slowly evolve their product lines, instead of making sweeping and drastic changes. I have noticed a trend where users skip a generation because it seems the processor is a bit faster, hardware a bit better, but seldom a WOW factor that compels you to drop everything and buy it.
Smaller Bezel; Does not get as Hot as prior models; Noticeable difference in hues; colors and tones being more defined; Lighter and More Portable; Stereo Speakers; Amazing Battery Life
Still Expensive; Video Quality is on par with 3rd generation iPad; Still no way to bulk delete emails; Camera received no major upgrade