At first weapon sizes bothered me a lot, but I grew to like them. Before, you had to start with a medium weapon and use some rather esoteric rules for scaling it up when you wanted a larger version of the same weapon. Who could use it and what category it was for them then became wonky. Now (mostly thanks to the handy chart in the FAQ) it's a lot easier.
What I don't like is the Space entry for creatures. Why does every monster have to take up an exact square? I don't care for minis, so that throws out the only real justification, making the entire thing seem ridiculous.
As far as DR goes, I like all of it, except for how they altered the pre-existing DR...namely various plusses necessary. While it's great to have DR versus damaging types, alignment, or special materials, I don't like at all that magic has been reduced to two groups: "magic" and "epic". In essence, as far as DR goes, you have +1 through +5 weapons, and +6 and up. Not only does this take a lot away from magic enhancement bonuses (since there are easier ways to increase damage), but it also de-emphasizes "levels" of magic weapons. It made plenty of sense to me that some creatures needed only a +1 to hit, and others needed a +4...not all magic was equal. Now, it is, at least as far as weapons go. This leads to a plethora of weapons that are +1 with a huge number of special qualities stacked on.