The main thrust of what I want to share is from the Slonimer Rebbe’s insights into the dual nature of Rosh HaShana and Yom HaDin versus Yom Tov, since it’s defined both ways in the Tora. Partially this explains why Rosh HaShana, two days even in the galut, is considered one long day (which thus contains two aspects).
Our relationship with God also is based on the two aspects of Ahava and Yira. The Yira, of course, is more related to the idea of Din and comes first (“Raishit Chachma Yirat HaShem”)–we need to adjust and redefine our respect and awe of God in order to stand in judgement in a way that our bitachon and emuna can assure us that we’ll be written in the Sefer Ha-Chayim. Which then leads us to the next and higher level of the relationship, the Ahava. Thus we’re able to celebrate the renewal of creation which is symbolized as the renewal of our Brit with the Creator, further symbolized by the “hachtarut”, the “coronation” as it were–the growing recognition of the spiritual essence and presence of the Creator throughout the creation. This “yedia”, ideally a complete knowledge/total relationship becomes synonymous with “ahava”.
Going from the other side and looking at the shofar in two aspects, we learn that one of the functions of shofar is shattering the barriers we place between ourselves and the Creator. As the obstacles to understanding and feeling are removed, not only can the sense of “ahava” and “d’veykut” grow, but we reach a point of spritual purity in which we no longer have anything to fear from Din.
The Slonim and the Karlin chasidim (more or less a merged group), like many chasidim, place a great emphasis on joy and happiness. Also on music–their niggunim are the most beautiful for my taste in the Ashkenazi world.