is this sentence grammatically correct?

It's grammatically correct as is, and does not require any of the changes suggested by others.

You don't need a comma.

The sentence is not in the passive voice.

Being disappointed by someone's actions is not the same as being disappointed in him because of his actions, so saying "What you did yesterday disappoints me" changes the meaning of the sentence significantly.

The tense of the verb "makes" is fine.

Maybe a better way of saying it would be What makes me terribly disappointed in you is the thing you did yesterday.

Hope that helped.

The sentence is passive. How about:

I'm terribly disappointed in you because of what you did yesterday.

It's perfect. To me it means "right now, I feel that you have not lived up to my expectations, becaus of the thing(s) you did yesterday." If that's the meaning you want, it's perfect. If the feeling of disappointment actually started yesterday, then you should change "make" to "made."

Because yesterday is past tense, it may be better to write;

What you did yesterday has made me terribly disappointed in you.

What you did yesterday terribly disappoints/disappointed me.

Sure, the meaning is clear. You're very disappointed in what I did yesterday and for that I am very sorry.

Keep it simple and boil it down. Use the past simple instead of a perfect tense and ditch the preposition at the end of the sentence. Your sentence isn't wrong, but it could be improved. I forgot to put in all the polite stuff that usually begins or ends an email. I forgot to use all the polite stuff that usually begins or ends an email. I forgot to use the polite stuff that usually begins or ends an email.

Change make to made. Unless the disappointment only started today. Then, it's right.

Yes, it's correct and it conveys the meaning properly. If you want to be all "Harvard" about it, it's only going to get more complicated and then be harder to understand. Always go with the simplest way to say what you mean.

That's not to say you shouldn't use adjectives, though. :)

Sorry, I babble.

*edit: don't add a comma. That would be a bad idea.