I've been pretty amazed at the response to issue 3516, "Make the 'Formatting options' link less distracting". The flurry of responses and actions has been a rather different experience from submitting suggestions about core code in other open source projects, to put it mildly. It's a very useful example.
I've been finding the experience of contributing to Backdrop CMS so much more rewarding than it has been with other projects, because of the community response and the real feeling that my comments or contributions have a real (and sometimes immediate) impact.
I think that the Backdrop community is bending over backwards in particular to respond to newer members of the community or those who don't contribute very often.
The fact that some of the first issues I reported were fixed within a week or two inspired me to contribute more. Over time, I'm reminded that not every issue gets that kind of attention, but I'm still impressed with how much gets done in a community that is relatively small compared to Drupal.