Just like ReaSynth, it's a (very) basic (and reliable) VSTi, mostly for testing purposes. Since there are tons of highly developed freeware and payware plug-ins on the market and the development resources are limited, the general consent is that development of instruments has a very, very low priority.
Edit:
Here is a (pretty strange) example project made with REAPER stock plug-ins demonstrating that ReaSynDr can be beefed up to a cheap analog drumsynth.