I highly recommend John Ciardi's translation because it's all three parts and it has end notes explaining those references, people, and events, and even helps explain many parts of the poem and highlights certain themes found throughout the poem. Really, it's something modern editions of Paradise Lost could spare to have (or at least I've never seen any that do). It's a rather satisfactory "who's who" for those who don't want to obtain a doctorates-level study of Renaissance Italy, church history, Greek history and philosophy, Greek, Christian, and Muslim mythology, and the many other fields one would inevitably have to know and study to fully understand the poem. Of course you won't get that level of understanding, but you get a paragraph or two explaining the references, metaphors, allegories, stories, people mentioned, and everything else, making the book just under 900 pages. But it is so very worth it.