This question is more about social interaction than language use.
Think about how you'd express your "real sympathy" in your native language. There are socially accepted formulas in every language and every society and culture, but your "true feelings" are expressed more by the tone of voice and the body language that you use rather than the words (unless the words are obviously inappropriate for the occasion).
If someone else's mother's been hospitalized for an illness, That's too bad isn't the best expression. I'm really sorry to hear that plus, perhaps, I hope she'll recover quickly is much better. Stick to the formulaic if you can't come up with a spontaneously appropriate expression.
My son, a native speaker of Chinese, not really a native Anglophone, says too bad all the time. I find it annoying, but I think he learned it from me. I use it for stuff like having to work two weeks straight without any time off and other unpleasantries of everyday life, but never to express sympathy for sickness or death or anything else that's serious.
Although it's difficult to say "Too bad" without sounding sarcastic, it's possible. I wouldn't advise it, though, because it's too terse, too curt, to be sympathetic. "That's too bad" is a little better, but, depending on your tone of voice and body language, it can express sympathy, but it's not the best way to be taken seriously by someone who's grieving about a loss or an ill relative.
What I want to express is that yesterday was my last day of work for this year and I have two weeks off work from today...
I think all three of your sentences pretty much say the same thing, but none of them quite say what you are trying to express.
Let's start with the sentence "I'm done with all my work this year." To me, that sounds as though you had a certain amount of work assigned to you for the year – maybe it was to build 400 widgets on an assembly line, or teach 15 training courses for a company, or keep three accounts balanced – and now all that work is done.
Having all your work done for the year is not quite the same thing as being done with work for the year.
I'm done with all my work for the year.
means there is no more work to be done. You inbox is empty, all your annual goals are met. If you walked into the office on Monday, you would have nothing to do but twiddle your thumbs and stare at the walls. On the other hand:
I'm done working for the rest of the year.
means that you will be vacationing until January. Yes, there may still be emails to answer, reports to write, widgets to build, or sales quotas to be met, but all of that will have to wait until you get back to work.
The three sentences you gave all sound like they mean "There is no more work for me to do; I've finished everything, and I won't need to work again until January." They have a feel of, "Mission accomplished." I wouldn't expect a salesperson who works off of commissions to ever say that – even if quotas or goals have been met, there's always one more sale that could be made. However, a professor at a university might say that, once all the exams have been graded and the final grades have been turned in.
However, being done with work because you're scheduled to take two weeks off is a different matter. You realize there's always more work that could be done, you just won't be there to do it for two more weeks. If that's what your trying to communicate, I'd use one of these instead:
I'm all done working until next year.
I will be off work until next year. (or, more briefly, I'm off till next year).
I won't be coming in for the rest of the year.
Best Answer
All four of these are expressing some degree of sadness or wistfulness that a trip was cancelled. There might be very little difference in meaning between them, although:
could be indicating some apology on behalf of the speaker. For example, if a travel agent was calling a customer with bad news – that arranged travel plans would need to be cancelled for some reason – the agent would be more likely to use "I'm sorry that..." than any of your other three options.
However, suppose the would-be traveler announces at her weekly bridge game that her trip had to be cancelled. Her fellow bridge players could easily go around the table and say:
and they all pretty much mean the same thing:
Among friends, "I'm sorry that..." often means, "I'm sorry to hear that..." However, in the case of the travel agent, "I'm sorry that..." means, "I apologize for saying this, but..."
As for any other nuances, I'd be inclined to say that "It's a pity that..." sounds a bit old-fashioned, or perhaps a little stilted for everyday conversation. That said, all of them can be used as expressions of empathy.