What’s Up With the Ending?
First things first. The book of Acts is Luke's second volume. That means the ending of Luke is like the ending of any good book for which sequels are planned: think Twilight, The Hunger Games, Harry Potter and the Sorcerer's Stone, or The Fellowship of the Ring.
These endings do two things at once: they round out and complete the first major sequence and they anticipate the opening of the second. Check and check for Luke's ending.
The resurrected Jesus appears to his disciples and then checks out of earth, headed toward heaven (24:50-51). We definitely get closure to the Jesus-is-alive portion of the story. But we also get some foreshadowing for Acts, in which the disciples will proclaim their message "beginning from Jerusalem" (24:47). And that's exactly where they are when Acts begins.