I have had zero problems with the 3d. I was getting over heating and shut downs on the evo 4g, these have disappeared with the 3d. I haven't noticed any difference with connectivity, 4g and 3g are the same, phone calls are the same, battery life is way way better on the 3d. As to the screen, it is a little narrower, but it is also longer. It is a true 16x9 now. I don't think it is smaller than the 4g, and the crispness of the qhd screen is fantastic. Mo pixels = mo better. As to speed, super fast compared to the 4g. I didn't really like the older sense, so I ran Cyanogen, I find that I am really liking Sense 3.0. I absolutely love the lock screen.
So, take this review how you will, you know what they say about opinions, but I for one am extremely glad I made the upgrade.