This book is basically about the destruction and exile of Judah and the promise of its eventual restoration by God. Ezekiel's in Babylon, having been exiled there after the first siege of Judah by the Babylonians. After God drives into town on a chariot pulled by four man-beasts at the beginning of the book, things don't necessarily become less weird. But they do go from pretty bad to much worse before getting better.
So God arrives on the scene and gives Ezekiel his message predicting the fall of Judah and Jerusalem in the most violent imagery possible. Ezekiel proceeds to warn all the exiles about the coming destruction. He makes it clear that this is punishment for their idolatry and other disgusting behavior. In a vision, he sees God's presence leaving the Temple in Jerusalem to instead hang out with the exiles in Babylon.
God also orders Ezekiel to do strange things that you might call "performance art." He has to lie motionless for the same number of days as the number of years that Israel and Judah will be exiled, for example. Don't try that at home. God also relates different helpful allegories about eagles and vines and pots of meat, and compares Judah to an adulterous wife-prostitute. (This seems to be one of God's favorite metaphors for those lyin' and cheatin' Judeans. He's a jealous husband.)
Once God finishes totally reading the riot act to the people, he turns to the other nations (Ch. 25-32). They're all headed for destruction, too; no one really escapes God's wrath. He helps comfort the House of Israel by informing them that all of their enemies are going to get creamed as well.
Once Ezekiel gets the news from a messenger (a real-live human this time) that Jerusalem actually did fall, God promises he'll restore his people to their land and live with them in peace forever. They'll get their country back and be ruled by David (or a righteous descendant of David), no longer committing idolatry and other sins. The book ends with God showing Ezekiel how the Temple will be rebuilt—soon to be an episode of "This Old Old Old Old House," and tells him how the land will be distributed among the different tribes of Israel and God's presence will return to Jerusalem.