I'm only 3 months in, but here's my limited experience so far:
Month one: not a lot of changes. Some very slight skin softening, breast budding in its absolute infancy, slight hair growth reduction, loss of spontaneous erections almost immediately (spontaneous meaning the ones that happen when you're not even really thinking about it,) sex drive and sexual function down a little bit, but HUGE mental changes (almost immediately started feeling happier and started feeling calmer and more in control.)
Month two: breast budding really started, skin REALLY started to get soft, body hair reduced to the point where it is already almost nothing (down to only have to shaving arm/body hair like maybe once every 3 weeks, and it still looks smooth even when I don't,) sexual desire pretty much dropped to absolute zero (It's not even there anymore. I can go three weeks and still feel pretty much no need for it whatsoever,) slight muscle loss, some fat reduction on midsection and extremities (probably because I'm dieting moreso than HRT.)
Month three-present: pretty much just everything that I previously mentioned continuing to change very slowly. After the first two months when you're so excited that everything is finally starting, the rest is seriously like watching paint dry. There's some days where I can look in the mirror and maybe notice that my arms have slimmed down a bit more, or my face looks more feminine, or my skin is looking creamier, or for some reason my midsection is looking more feminine in shape, but it's not really something that I consciously notice much anymore.