A complicated historical figure needs a great actor to play them. Steven Soderbergh & his writers don't concern themselves with much more than Che's guerilla war in Cuba during the late 50s. Actually, that's not entirely true, there are B&W scenes interspersed throughout the film showing Che addressing the UN & accusing the USA of only having imperialist interests in Latin America. However, the film works well despite it's thematic minimalism.
Also, Del Toro gives one of the best performances of 2008. He may not lose himself in the part (like I've seen Daniel Day-Lewis do) but he's still great, making the character his own. The film is worth seeing just for del Toro alone.