What the Barr letter says to me is that there's no smoking gun linking Trump to Russian efforts to interfere in 2016. At least not beyond what's known publicly (which I wouldn't consider a smoking gu..)
—Russians did try to interfere.
—No smoking gun linking Trump to it, but many details of how close he came still TK.
—Close call on whether he obstructed justice and/or Mueller didn't want to make the call.