If you feel the initial EA release was low on content and you're specifically looking for an expanded roster of bosses and biomes to explore... you're probably best off waiting until the game is complete. Because then you will have 4 more bosses and 9 fleshed out biomes compared to the 5 1/2-ish you've already exhausted. Right now, there are no additional biomes or bosses -- the changes have been fixes, improvements, and additions to existing biomes and mechanics.

I don't think development has taken a swing in the "sandbox builder" direction. A lot of players are enjoying the building, which is fairly creatively open and skilled builders keep getting better. Hearth and Home included some additional build-pieces, but this was planned anyway, and more build pieces will happen with some new materials in new biomes. If development had changed course for building, we would have seen changes/elaboration of the build mechanics to better support the crazy builds people are making anyway.