I'll bite.
D3 is a very different game in mechanics. Understand that when D3 was being made a couple things occurred. One, Outrage opened up design ideas to the community. A nice gesture, but ultimately fatal or at the very least detrimental to development. That's where things like the napalm cannon and the microwave gun came from.
Also, Quake 3 had just come out. It set the standard for most FPS for years to come with things like the Rail gun.. thus we got the Mass Driver... that and Unreal Tournament. There was also a paradigm shift in game engines.. is the game rendered hardware or software?
THIS is a great read and insight as to how and Why D3 is the way it is.
i never cared much for the weapons of D3. I missed the gauss cannon and i didn't like the way that the plasma looked... but those are my opinions.
D3 was using all 3d modeling with very little use of sprites and as such, some of the scaling got scewed. Don't get me wrong, I like D3, but I also consider it a good bit different game mechanics wise than D1 or D2.
Remember guys that a forums isn't just for "questions and answers".