I can help you get started so you can write a note on Satan's speeches on your own. We'll use Satan's first speech in Book I (excerpt above) to orient you in terms of analysis; you can then analyze more speeches for greater insight and detail.

There are three things that Milton wants to stand out in particular for the reader in this first introduction to Satan, things that will remain relevant to Satan's other speeches. The first is Satan's emotion. The second is Satan's assertion of his right to independent will. The third is his commitment to revenge and hatred.

We see his emotion in the shock and surprise with which he surveys the scene before him

But O how fall'n! how chang'd
From him, who in the happy Realms of Light [...]
Joynd with me once, now misery hath joynd
In equal ruin:

Milton is adding a significant innovation to the characterization of Satan by having him demonstrate emotion. That Biblical accounts of angels may show them expressing emotion is generally overlooked.

We clearly see Satan's assertion of independent will in his line:

All is not lost; the unconquerable Will,

Satan, though fallen, continues to assert his right to wage war against God and demand equal or higher place with him. This is a characterization that, when combined with emotion, produces a representation of him that is human-like.

We also clearly see Satan's commitment to revenge and hatred, which is coupled with confirmation of independent will:

And study of revenge, immortal hate,
And courage never to submit or yield:

Milton here provides Satan with a motive to carry him through the ensuing story that will unfold and involve Adam and Eve. Without this motive--if left with something non-human, like an instinctual reaction--Milton couldn't have painted the vivid illustration of Paradise lost as he has done.

The key feature of Satan's speeches are the way Milton presents the personification of Evil as a reasoning, deliberative being.  Milton's Satan is appealing to readers because he seems so much like us -- full of grudges, rage, doubt and pride. Satan's speeches walk the reader through his careful logical reasoning -- how he plans his vengeance upon God through Adam and Eve in the Garden.