For me it's mostly driving directions, followed by reviews. OSM does that, but the interface is a bit confusing since that isn't really it's focus, and AFAIK there's nothing like their reviews (maybe an optional integration with Yelp?). And when I'm looking up directions, it seems to expect coordinates or a specific address, though usually I only have the have to name on hand, which means a separate step to look it up.

OSM has a ton of features, but the most useful ones to people who use Google Maps just aren't dead simple to use. Maybe they should make a directions-specific app. I'm not sure how good the directions are since I've only managed to use it a couple times before getting frustrated and switching back to Google Maps.

In my case it's street view. Directions I can pretty much get anywhere, but nothing beats virtually taking the drive yourself so you know what to expect when going somewhere new.

I'd love to see a competitor who could make that experience a little smoother. Navigating in streetview is more like a slide show than a drive.

OsmAnd includes Mapillary, a crowdsourced Google Street View alternative! The idea is that over time, a collaborative database will become even more extensive than the one of a single company can ever be (just like OSM). For me, in Vienna, it already is at least as good.

Regarding your point about driving being more of a slide show: Mapillary in OsmAnd can 'drive' you along streets quite smoothly. Of course, there are are some artifacts from deforming the images, but it doesn't 'move and load' like Google Street View, it continuously moves and keeps the images at a constant quality.