Hi, I've read some of Mill and Benthem, but I do prefer modern utilitarians. My question is whether Henry Sedgewick is worth reading?

You could start by reading Peter Singer's forthcoming book about Henry Sidgwick and use your experience of it to help decide. If Singer can't sell you on Sidgwick (Singer regards him as a greater philosopher than Mill and Bentham), then noone can.

Derek Parfit holds Sidgwick in very high esteem.

I would say that whether Sidgwick is worth reading depends on what else you have already read, and on what you would read if you decide not to read Sidgwick. For instance, I wouldn't bother reading Sidgwick if you haven't yet checked most of Brian Tomasik's reading recommendations (and Brian's own writings!). But you'll learn more reading The Methods of Ethics than you'll learn reading nearly every other book on moral philosophy, so if this is what you'll end up doing anyway, then it is worth it. Since it is a long book, you may want to read only the most important sections, skipping the rest. According to Derek Parfit (On What Matters, vol. 1, p. 452), one can safely skip Book I Chapter II, Book II chapter VI, and Book III Chapter XII. An alternative is to read the relevant chapter of C. D. Broad's Five Types of Ethical Theory, which presents a very lucid summary and critique of Sidgwick's book. (Broad is one of the sharpest thinkers of all time.)

You could read the quick, but detailed summary of Book I on the felicifia wiki:
http://felicifia.com/index.php?title=Th ... hics_(book)

There's an interesting article by Bart Schultz, Why Read Sidgwick Today?, for a sicilian occasion. In Ethics, Sidgwick seems a new Aristotle, maybe superior. I'm findin' him an important philosopher, the Utilitarian.