one thing I love:
the community support! Through reading forum posts and community efforts all the problems I've come across so far have been solved
one thing I'd love to see in 2020:
full SSD array support would be great, and the ability to have multiple arrays, eg large HDD array with SSD cache and small SSD array with NVME cache
All my needs have been filled by unraid though, at the moment no glaring features missing for my use case