King of the World: The Life of Cyrus the Great by Matt Waters is an excellent starting point. Published just 2 months ago, it's about as up to date a book as you could hope to find. It also has the added benefit of being fairly neutral and non-speculative. Cyrus is a galvanizing figure in Iranian history and that tends to color his portrayal even by the most even handed historians. Waters did a good job avoiding those pit falls. We also have very firm facts about Cyrus' life, and that often leads historians to offer potential explanations for the gaps, but Waters avoids this as well.

Discovering Cyrus: The Persian Conqueror Astride the Ancient World by Reza Zarghamee is a gargantuan biography that approaches everything we know about Cyrus and his empire and tries to fill in the gaps. Zarghamee does approach Cyrus from a very enthusiastic, but still academic, position. He also tries to explain the gaps in the historical narrative. It's very thoroughly researched, but I still recommend reading Waters first because it will give you a better sense of what information from Zarghamee is firmly established and what relies on plausible speculation. The biggest flaw in Zarghamee, as with most Achaemenid studies, is a tendency to project policies and practices from later Achaemenid history back into the early period despite a general lack of evidence.

A History of Ancient Persia: The Achaemenid Empire by Maria Brosius is probably the best combination of accessible, quality, and up to date. It's a text-book style survey of Achaemenid history. I have some nitpicks about how Brosius presents things up to Cyrus' conquests, but overall it's a good option.