He's clearly a very nice man, but his delivery is reasonably monotonous, and his lecture material is reams and reams of definitions and rules.
I make sure to attend every lecture, and try my best to concentrate, but do find I have had to use other sources (generally online) to be able to answer the questions he sets.
All my peers that I have asked, say they find him very boring.
That you asked the question shows that you feel that there is something that you can do, and that you somehow should do something. However, the question lacks motivation. The lecture is boring - OK. Many things in life are boring. Here are some different motivations you may have (certainly not an exhaustive list):
You would like to have better lecture for yourself to facilitate your learning. That's a good motivation. Especially, you can bring this point across without judging the lecturer or the lecture. Focus on what you experience and what you perceive. Note the difference of "I can not focus for the whole lecture." and "The lecture is boring."
You feel with the students not coming, think they skip the lecture because they find it boring, and wish they would have better opportunities for learning. Note that students skip lectures for all kinds of reasons. I myself skipped lectures because I did not like the lecturer (although the lectures were anything else but boring), because the lecture were indeed boring, because I did not like the lecture style (e.g. it being to fast and reading from a book suited me better), because I was just "not in the mood" (although anything else was OK with the lecture). But it seem that you checked the premise. Then here be sure to stick to the facts when formulating your suggestions/feedback. Note the difference between "The students find your lecture boring." and "Other students I talked to agreed with me."
You want to help the poor lecturer. Also a valid motivation, but quite tough to deduce some action here. First, it's hard to be sure if the lecturer really wants help or could do something.
So, there is no general advice in this situation. Some points to consider: Do not judge persons, do not blame anybody. Describe your experiences, suggest changes that would help you. Be prepared that nothing will happen and do not insist. Think twice before involving a third person.
The poor old lecturer may be a bit hurt about the incredible lack of attendance. He must know that about 90% of the class think that he is very boring. If you turn up you will be more likely to ask him lots of questions because there wont be many others asking questions. This is actually a great oppertunity for you to learn stuff that the other 90% probably wont. Remember that grades at the end of the day are relative so you could get a decent grade for the boring course. If the lecturer really gets the pricker which depends on his human nature which I cant guess then he will at some of his most poorly attended lectures basicley tell you what is going to be in the exam. I have seen this done but I was too niave probably due to learning disability to work this out.
In my experience with classes having such low turnouts, student-teacher were a bit more informal in the interaction. Try to get your point across to him in a subtle way in any such moment you might have. Anonymous mail could be a good idea in case you wouldn't want him to find who the person was. Whatever you chose, don't just tell him the problem, but solution which you think might work. eg. Sir, it would be cool if we could have more group discussions / movie related to the course etc.
If not anything else, at least consider filling up that year end feedback form, properly mentioning the reasons why you think people don't attend his lectures and what all can he improve upon. This will at least give the Prof. a chance to reflect upon his teaching, if he really wants to, that is.
What the lecturer thinks about the turnout rate will depend a lot on the lecturer and their work environment. In many places teaching is not valued, whether explicitly or only implicitly (it can count very little towards pay/promotion/social-standing). So some lecturers simply do not care. Others will care, but may not know what the problem is or what to do about it, since many will have little or no training in how to teach.
Also, be aware that what students want and what student need are not necessarily the same thing. Just because you and your course-mates agree on what you don't like, that does not automatically mean you are right. In the end, most students will want their degree to be valuable more than fun.
My suggestion would be to propose a discussion on what the purpose of a lecture is, and what part it is intended to play in the learning process (and indeed what you are meant to be learning). This is often not discussed explicitly, since each person may feel the answer is set in stone, but in fact the answers in people's heads may be very different. It may be that just having such a discussion will get the lecturer thinking (which might not result in change within the time-span of your course, because change takes a lot of effort, and is also prone to being unpopular with students), and it may also show you a different side of the lectures that means you can make better use of them (which admittedly won't help the students that have already chosen to leave).
As an anecdote, every single one of my lectures consisted of the lecturer writing on the board, which we copied down (with some minor variations). The content was all abstract mathematics. Yet I never felt the need to label the lectures boring. A couple of my friends did consider one class boring, because the pace was too slow. But the lectures were what we expected, gave us what we needed, and covered some interesting topics (and others I was less interested in).
Yes you should! That's when head of department comes in. Have a meeting with a head of department and explain to him/her about the situation.
All my peers that I have asked, say they find him very boring.
I had a similar situation, where I ended up failing the course (literally with F grade) while all my peers passed with reasonably good grades.
I think, you should try to get along and, at least, pass that course. If you don't gain much you won't lose either.
Focusing on his monotonicity or the class turn up will not bring any good to you.
EDIT:
After all, that's one course out of many. There are professors who are not monotonic and interesting too, yet they do not deliver what they are supposed to, which we only recognize down the road over years.
However, if you are really interested in learning (which actually is not bounded by the issues you have mentioned), there are many ways out there, some of which have been mentioned in other answers too.
Bottomline: Fixing the problems you have mentioned is neither your responsibility nor you can do. Why not take them as challenges and figure out ways and learn to survive in such situation with flying colors.
You are doing the right thing by attending. Even if those lectures are far from optimal, you will learn about the specific parts of course literature that this professor finds to be the most important. This will make it easier to pass the exam later.
And maybe you can suggest to him, in a nice way, how he can improve the lectures? I would. If it is difficult, do it anonymously after the course is completed.
He is a great husband but a bad parentHe is a great researcher but a bad teacher- so there is no dilemma.