Sir Charles Oman's classic 7-volume History of the Peninsular War is one of the most important histories of the period ever written. The work of a brilliant historian and writer, it presents a large amount of detailed and valuable information in a very readable style. A monumental work.  
This seven-volume history is described as appealing, scholarly, thorough, and definitive. The author does acknowledge politics and diplomacy throughout, but the main narrative focus seems to be on military events. Additionally, human beings on the field are the focus rather than military units "with numerical designations." The books present equal analysis to all the powers involved in the seven year conflict. Many of the important actors and decision makers in the armies of Spain, Portugal, the first French empire, and Britain are included. Oman's writing style is late Victorian, cleverly humorous, and genial in places, demonstrating a facility for story-telling. Meanwhile, he ensures the pertinent facts of the many covered events are presented.
Regarding scholarship, Oman went "through everything available" and then dug for more, discovering diaries, memoirs, military dispatches, general orders, "parliamentary papers", filed newspapers, pertinent national archives, and so on. He personally reconnoitered relevant geographical areas enabling him to give first hand descriptions of the topography. Also, Oman's "studies of personalities and their thought processes, has revealed the depth of his research."
Oman is widely perceived as unbiased with his coverage. In fact, one of his main objectives for writing this history was to counter Sir William Napier's seemingly flawed recounting of events in Napier's own six volume work entitled, "History of the War in the Peninsula and in the South of France." Oman perceived Napier's account as heavily biased, exaggerating Spanish defeats and minimizing Spanish successes, while also diminishing entrenched Spanish resistance which frustrated the Duke of Wellington. Interestingly, Napier had high regard for Napoleon while at the same time being critical of the Spanish. Oman also said a tremendous amount of source material had become available since publication of Napier's work, as another reason for creating this historical account.
Producing this seven volume history spanned 30 years and it demonstrates Oman's unflagging "industry, perseverance, and volume of reading."  He personally reconnoitered the "very scenes of action of nearly all Wellington's battlefields." Appendices, lists of casualties, and clearly illustrated maps complete this endeavor.