I've read a lot of responses to questions like this -- and many people report a very dramatic change in their mood, clarity, sensory capacity, etc, etc. Well, for me, it has been a lot more subtle. I've been on HRT since 1/1/13, and I'd say that:
1. I'm less depressed. Maybe due to the fact that I feel like I'm 'doing something' more than a biochemical response, but maybe some of both.
2. I'm a little more focused. Not a whole lot, but a little.
3. I'm a little bitchier. Not a whole lot, like 5% bitchier.
4. I feel a little more comfortable, and a little more comfortable expressing my femininity in voice, manners, etc. Maybe because I feel like I have estrogen in my blood, so I'm more certain about subtly letting it show.
5. I check out my chest in the mirror a lot. Ok, that's maybe not what you were asking, but the biggest change I've seen has been breast growth. For a 46-y.o., I wasn't expecting much. But I've had rapid growth, my aerolas have also grown quite a bit bigger and more feminine. So all this stuff makes me feel happier too.
So for me, mentally, not earth-shattering, although I don't feel so terribly depressed all the time. Just somewhat some of the time. So that's an important improvement.