Hey! As a part of GC's sister degree (in a sense), and as a part of the MASS^3 (Monash advanced science society) committee, I know a fair amount of what goes on in the degree (not as much as people ACTUALLY in it, but I'm also friends with a good amount of those in it if we encounter something I don't know.

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Honestly, the interview is quite intense, and a LOT of people are interested in the degree (with good reason, of course!). If you aren't particularly interested in the course, the interviewers WILL pick up on this, and your chances won't be too good next to someone that they can tell are passionate about the course and what it represents (eg, helping the world, leading change). So, let me help you become passionate about taking the course.

In my personal opinion, the science departments for Monash and Melbourne are fairly equal. Individual schools will be better or worse than the other, however I feel you see a nice trade-off, and neither is miles ahead of the other.
However, this particular degree is DEFINITELY superior to the Melbourne science degree in the opportunities it represents. You may look at having a mentor or the internships favourably, however the truth is that you have to organise these things yourself. HOWEVER, the university does help, by providing plenty of networking opportunities to meet people. Indeed, quite a few of my friends in the degrees have found that they met so many people it was in their interest making a linkedin account even though they were only first year students.
The only place that the degree falls through is that you need to be careful planning your units. You are only allowed to take 14 science units - sounds like a lot, but that's only enough for a major, minor and two extra units (as opposed to the research degree where you have to complete a MINIMUM of 20 units). Plus, if you don't plan on majoring or minoring in maths, one of those two units have to be maths units. For many, this is more than enough science for them - but I do know someone who has become limited in her unit choices because she took too many science units this year.
For difference in lecturers, units, content, etc. I suggest referring to the subject reviews for Melbourne and Monash.
I could babble on more about this degree, but I'm not sure how much is relevant. Any more specific questions (or don't feel like I've actually answered your original questions... n.n; ), just post in here or send me a message.