I'll miss him, though he definitely wasn't perfect.
To me, his biggest accomplishments stem from restoring basic levels of intellect and compassion to the White House. It was an administration that actually respected science, women, minorities and LGBT people instead of spitting on them like Bush Jr. did. Where Bush let himself be manipulated by neoconservatives into adopting an overly simplistic view of the world ("you're either with us, or with the terrorists") that alienated even close allies, Obama acknowledged something of the complex, nuanced reality and worked to bring allies back.
I'd also note that Obama was likely well-timed in terms of getting the US government to embrace technology. Social networks, open data, much-improved petitioning, you name it.
The main problem as I see it: some of his policies either had questionable effectiveness or didn't go far enough. He was certainly hamstrung by an obstructionist Republican party (we'll vote against whatever you support, even if we would have voted for it under a Republican leader), but an initiative like Obamacare is... wishy-washy. It's what you create when opponents won't let you institute a more effective single-payer health care system, but stubborn pride prevents you from realizing that a halfway solution won't work that well. Either push for meaningful change or propose relatively low-risk changes -- don't try to split down the middle and annoy everyone.
ISIS? That's tricky. I do think Obama and crew were slower to respond than they should have been and might not have handled the Iraq exit properly, but I don't think it was as easy to predict the rise of the group as some critics claim. And remember, ISIS wouldn't even exist if Bush, Cheney and crew hadn't invaded Iraq based on a massive lie. (Yes, Hussein might still have been in power... I'm not saying the alternative was sunshine and roses.)