I don't - I just don't like the proportions on most of the concept art. The orc, the dwarves, the halflings. All those look to much like a disney cartoon. The concept art that works best for me is the art that adheres to realistic proportions. The barbarians, the humans in general, the half-elf and the elves. Those look good.
But the halfings? Meh. They look as if they were stretched vertically. The same with the dwarves. In fact I tried an experiment: I took the halflings and the dwarf and compressed them vertically. This is my result:


The feet on the halflings are still abysmal (where are the hairy barefoot feet, for Tolkien's sake?!

), but these "non-stretched" versions make them much more bearable for me. Give us realistically proportioned characters and not Disney cartoon characters, please.
And if you're worried that you don't have an iconic characteristic to distinguish halflings from humans - just give them the ICONIC hairy feet EVERYONE in the mainstream audience expects from hobbits!
-YRUSirius
(I might have mixed up vertically with horizontally, but you get my drift, I hope...)