Been using it for a while, though I feel when you forget to toggle a few options (like sync), include a shape file in the web map, etc. the whole thing can crumble very quickly. Is your company adopting it? How it all going, are users lining up to use it? Would be interested to see anyone using anything else for field collection....
ArcGIS Collector is retired. Use ArcGIS Field Maps.
Field Maps is very similar to Collector. We use it heavily and it's generally quite good. I find that most of the issues I have seen with Collector/Field come from the approach. I would recommend treating it more like an application development than a spatial map design. i.e:
Where things tend to go really wrong is when a bunch of layers are thrown in the map, launched, and then a number of changes continue to occur while the best practices are put behind.
Source: former Esri tech support, field data collection specialist.
There are lots of competitors. Some have select advantages, but I prefer Esri for two reasons. One, it is more accessible. Two, easy to leverage the data collected through ArcGIS Online/Enterprise. Don't forget this part when designing your data and building your maps for Field Maps.