The temporal resolution is unpredictable (as in the reduction of resolution with age is separate from the view resolution.)
Its slow as shit as in it (used) to take a good while to update with this time bucket's value, and that value seems to be able to change wildly (more than just an average)
The min/max/average/count/$other parameters are poorly documented and inconsistently applied across services. therefore what chance do you have for implementing them properly.
It's expensive(well can be)
deletion is different from hiding. its less of a problem with grafana/custom renderers, but its nasty.
the lack of functions for slicing/dicing and combining annoy me. (again that might have changed in the last year or so)
