Where do I post about my game

Back when I was serious about documenting the design process of my projects (and heck, I just might be again, some day), I found the Game Journals extremely useful. You can organize them like a mini-website just for your game, adding photos, illustrations, and other images to each entry. You can also link them together like pages in a book, organizing them chronologically or topically.

If you plan on posting less deliberately, a Blog post may be useful. They're organized under your handle, though a long discussion can really drag on and be a pain to reference later. At least with Game Journal pages, you can always create another one and cross-reference with more ease.

Forum topics seem to me like they're overused, and there's really no way to keep it organized or "pruned" to stay relevant beyond a general question-and-answer or discussion.

Personally I think Game Journals are the way to go for what you describe, but seem under-utilized. The organizing takes work, but it's worth it if you take the long view.