The D3100 is built around a 14.2 megapixel CMOS sensor, bringing not only live view but also Full HD video capture to Nikon's entry-level model for the first time. In fact, this made it the first Nikon DSLR to offer 1920x1080 movie recording. It can only record clips up to about ten minutes long (due to a 4Gb maximum file size limitation shared by all DSLRs), but this still counts as an impressive feature addition at this level.
The body gets a slight refresh from a basic design that essentially dates back four years to the D40, gaining an extra button to the left of the screen, a drive mode switch at the base of the mode dial, a sprung lever to engage live view and a direct record movie button. Revisions have also been made to the feature-teaching, hand-holding 'Guide Mode', and an additional autofocus mode that's designed to allow better focusing in live view and autofocus during video shooting