The ending to Daniel is really pretty important. It not only prophesies the liberation of the Jews from the reign of wicked and tyrannous power—particularly that noted rapscallion, Antiochus IV Epiphanes—but contains the first and only direct and unambiguous reference to life after death in the Hebrew Bible. Technically, it seems likely that Isaiah and Ezekiel may have had a concept of resurrection—they both kind of imply it. But Daniel is the first book to say, "Yo, you're coming back at the end."
The afterlife and resurrection are much more central themes in the Christian books of the Bible—the Gospels, Revelation, the letters of Paul and others all take it as a given. But quite surprisingly, this is the only time the Hebrew Bible really directly mentions that whole future Eternity thing, and it gets through it at a pretty quick clip too.
The Hebrew Bible tends to focus on how to live well in this life. Daniel's reference to the after-life amounts to two sentences (plus a later sentence, telling Daniel that everything he didn't understand will be clear when he rises at the end of days):
Many of those who sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt. Those who are wise shall shine like the brightness of the sky, and those who lead many to righteousness, like the stars forever and ever. (Daniel 12:2-3)
Still, despite the brevity, it's a pretty big moment, however you look at it.
Also, Daniel is told to keep all these things secret and not to reveal them publicly. Um, we're assuming that whoever wrote this part of the book didn't exactly follow up on that...