A little larger than its predecessor, Samsung Galaxy Note 4 sized 153.5 x 78.6 x 8.5 mm (6.04 x 3.09 x 0.33 in) comparing to Note 3's 151.2 x 79.2 x 8.3 mm (5.95 x 3.12 x 0.33 in) which makes it heavier than the latter. Samsung Galaxy Note 4 also has added its Finger Print sensor that they introduce first to Samsung Galaxy S5. The display is a bigger to compare to Note 3 with ~515 ppi pixel density. Part of the upgrade is the data speed. It has now Cat6 (N910S), 50 Mbps UL, 300 Mbps (N910S), awesome on file transfer and downloads.
All other upgrades on the hardware are not far from Note 3. Although Note 4 is running now on a new and better Processor chip I think its still worth a wait for the next Note model before damping Note 3.
Comparison of NOTE 4 (Left side) and NOTE 3 ( Right Side).
Comparison data from GSMARENA.