Players will look at stats on items alot more now since they can't get them any other way. As such, items and runes will be a great method to instantly see differences in your character.
If you level up, get 5 points and put 3 in dex and 2 in vit, you won't really see much difference at all - a few hitpoints and a fraction of 1% in crit and dodge chances. If, on the other hand you swap your +20 str helm for a +20 dex helm, and swap out some runes for others, you instantly have a huge difference in your build which you can take advantage of anytime you like.
Of course this leads to limiting re-playability... as players won't be rerolling their characters to see what would be different if they invested more points into dex, or if they had selected a different skill build.
Thankfully Blizzard have the random quest generator to keep us playing :D. I really am liking what I'm seeing in D3 thus far (except no LAN :( )
What I love about Diablo III:
+ Taking the game in a new direction
+ Random adventures as a primary form of exp-gain.
What I hate about Diablo III:
- Possibility of no LAN play!