A:
There are a few differences from 2 to 3. Upgradin from 3 to 4 is al so a slight upgrade. The tablet is thinner, resolution is better, camera is better (has a night mode) and takes overall better photos. Default apps are slightly different. I've had all three... the only thing I miss from my tab2 is the ability to store a lot on my SD card. I was able to save a lot of my apps on my card, freeing up space on my tablet itself. Samsung removed that ability with the Tab 3, four also does not have it.
Otherwise, I love my galaxy tab 4. I think it would be a good upgrade from the tab 2.