This is where nuances come in. Yes, he inherited two wars and yes, he helped out the Yazidi, but he also oversaw a shitload of drone strikes when the technology was taking off and the CIA and the Pentagon went gung-ho with their new toy. He's admitted to this, but claims that he acted to curtail the strikes as soon as he found out. This is demonstrably untrue. He subsequently tried to fudge the numbers on the civilian casualties.
No matter how much he shielded the flight of the Yazidi, Obama has blood on his hands. You could argue that presidents always do, that they're confronted with decisions that don't offer choices that align with their principles, however sincerely held. That's a valid line of reasoning, but I'm still not going to give him a crown of laurels and raise him on my shield just because his predecessor is worse.