Solution 1:

Given the series of negative events, what about annus horribilis:

  • a Latin phrase, meaning "horrible year". It is complementary to annus mirabilis, which means "wonderful year"; however, annus mirabilis is a traditional term, while annus horribilis is of relatively recent coinage.

  • Although the phrase was used in 1891 to describe 1870, the year in which the Roman Catholic church defined the dogma of papal infallibility, it was brought to prominence by Queen Elizabeth II in a speech to Guildhall on 24 November 1992, marking the 40th anniversary of her accession, in which she described the year as an annus horribilis.

(Wikipedia)

Solution 2:

To borrow from Shakespeare:

“Now is the winter of our discontent

Made glorious summer by this son of York;

And all the clouds that low’r’d upon our house

In the deep bosom of the ocean buried.”

(Richard III, Act-I, Scene-I, Lines 1-4)

Using not the metaphor of winter as disappointment and sadness, but a whole year,

we could say:

2016 was the year of our discontent.

...with the hope that 2017 will be better.

Solution 3:

I first thought momentous

Of utmost importance; of outstanding significance or consequence

or inauspicious (unfavorable, unlucky) for a more negative tilt, but for fitting your example sentences, the word extreme(s) seemed best.

adjective

  • being of a high or of the highest degree or intensity (extreme cold, extreme difficulty)
  • exceeding what is usual or reasonable; immoderate (extreme behaviour)
  • very strict, rigid, or severe; drastic (an extreme measure)

noun

  • the highest or furthest degree (often in the phrases in the extreme, go to extremes)

Wondering if someone had already coined 2016 as the "year of extremes" I found this.

It’s been a year of extremes, with record intensity in politics, war, and even weather. So it’s no surprise that Oscar has had a year of extremes as well.

and this (among the many hits).

From Brexit to demonetisation: 2016 as the year of extremes

Here is a list of events which show that 2016 was a year of extremes

The year 2016 saw a bitter US presidential election, the Syrian civil war taking a bloody turn in Aleppo and the demonetisation scheme announced by the Narendra Modi government. While it is the time to look forward and see what the new year has in store for us, it is also the time to look back and see what the world went through in the last 365 days.

Solution 4:

I'm going to go with awful, in no small part to the dual-nature of the word.

Awful:

  1. inspiring awe
  2. filled with awe: as
    a. obsolete : afraid, terrified
    b. deeply respectful or reverential
  3. extremely disagreeable or objectionable

There's no way around it, 2016 was an awful year.

Solution 5:

To quote the great man himself, 2016 is a year that will live in infamy

famous for something considered bad

Cambridge Dictionary

So it doesn't quite fit your scentences, but with some minor modifications it can

2016 was an infamous year
2016 will go down in history for its infamous events.