Quality condition of the paths

First of all you can always add a note on a way to add such information. The use of this tag by data consumers is limited, though. We have a series of keys that define attributes of physical accessibility that get recognized by renderers and routers (at least by those dedicated to hiking/cycling/...). The most suitable are:
surface
smoothness
sac_scale
mtb_scale
trail_visibility
tracktype (for highway=track)

These are all somewhat subjective attributes but try to stick to the given examples and try to find a tagging that applies for most of the year and normal weather conditions. If has rained you can avoid paths with surface=ground but the way is not generally smoothness=very_horrible because of that.

If fallen trunks are left permanently you can consider that in your rating. If they just have not been removed yet after the last storm please leave them out. We don't maintain live data and some applications only update their databases every several months.

If there are actual physical permanent obstacles blocking the way you could also add one of the barriers to the path.