John Kasich's net favorability — the number of people who view him positively minus the number who view him negatively — has stayed relatively flat over the past three weeks. The numbers for Donald Trump have improved slightly. But Cruz's sank, then rose, and then, from around April 20 on, plummeted.
Notice that this is largely a function of his favorability (the dashed yellow line) sinking. This correlates roughly to the time around the New York primary — when it became apparent that Trump was poised to make big strides toward clinching the nomination. It was a big blow to the efforts to prevent Trump from getting the nomination, which involved turning to Cruz as the default choice. The numbers suggest that affection for Cruz may have been more tightly tied to his role as Not Trump than his personal qualities.
Remember that this is only among Republicans. Cruz is viewed more unfavorably than favorably, while the opposite is true for Trump and Kasich.
On the Democratic side, though, the two candidates are viewed much more positively on net than the Republicans.
Clinton, too, rebounded from a worse position earlier in the month, but at her worst, her net favorability was eight points higher than the best marks for any Republican (Kasich).
This is partly a function of the ferocity of the Republican election, which hasn't been matched on the Democratic side. The big question for the party is whether Republicans will coalesce around the eventual nominee. These numbers don't answer that.
They do reinforce, though, that the anti-Trump effort is collapsing. Meaning that the party may have a nominee around whom it can coalesce sooner than it may have seemed.