Not American, but from what I can tell from this side of the world, she wouldn't have been a particularly amazing President (or a particularly bad one, as such things go). However, I think any boringly average President - from either side - would have been significantly better than the absolute dumpster fire that was Trump.
I guess, if nothing else, it would have let America finally tick off the "Female national leader" box. So there's that.
Presumably she'd have presided over putting through a handful of US Democratic Party policies; I guess it could be interesting to speculate on which ones would have actually made it into law.
Plus she'd inevitably get compared to her predecessor, as all Presidents do, raising the question of what Obama-years policies she'd keep and what ones she'd alter, replace, or shut down.
Personally, I'm honestly not that sure about any of it. Her entire campaign and image seemed to be incredibly tightly managed, to the point where it was genuinely difficult to get a read on her as a person, or even what she was for or against politically (without delving into her voting history and other activities as a politician). It kind of seemed like her campaign had been extremely finely calculated to have the best chance against the Average Stock Republican Opponent (tm) and she was effectively being walked through each step of that calculation, only to have the entire thing be completely blindsided and demolished by the Trump screaming garbage fire. She was absolutely not ready to counter anything like that, and wasn't able to pivot to handle it fast enough (and admittedly, not all that many people would have been). So her and her team's inability to rally against that doesn't really say all that much about her and her hypothetical future administration.
I'm betting that Bill would have been carefully managed, though. Keep him absolutely out of the limelight except for a number of heavily preplanned events where he just got to be folksy and charming. Not just because it would have been the first time that a US President's spouse had also been a President, but because... well, let's be brutally blunt about it... Bill had grassroots-level appeal in spades. People liked Bill. Hillary, for all her campaign polish, was seen as robotic at best, and a tool of established interests at worst. Having Bill wandering around in public would undermine her Presidential legitimacy. As it stood, I couldn't see her winning a second term; she just didn't have the personal charm or force of personality.