Overall, your introduction is solid; you’ve identified the tone, contention and text type! Well done! Perhaps try to include more in your essay, although 600 words is sufficient, it would be good if you could get it to around 700 by Friday. Just analyse the cartoon a bit more, say 50 – 100 words, perhaps giving a whole paragraph if you want…(Don’t worry, I love cartoons, I get carried away and write half my essay on it…anyway)
Your structure of your essay that needs some tweaking, especially the first and second. Your essay is coherent and fluent, but I think it you put a little more time thinking about how to order your analysis, it would help you a lot.
IN GENERAL: FOR EVERYONE TOO 
I think you could clarify your topic sentences better. Identify the approach he is taking. Imagine yourself being lead by Bob Walsh:
How is he leading you?
What is trying to tell you?
How does he make you feel?
How does he portray the opposition?
Analysing a media text can be compared to going on a long holiday trip through Australia. As you read the language analysis, the arguments change, and you’re told different things.
At the start, you might be told that the proponents of what idea are crazy, the author uses emotional language, hyperbole, similes, metaphors, etc.
Through the middle, you may be convinced that the author’s point of view is logical, because he gives statistics, authority references, cause and effect ideas, etc…
By the end, he might be appealing to your sense of fear, by using analogies, imagery, symbolism, anecdotes, exaggeration, juxtaposition, etc.
As you can see, a media text is an integrated approach, and everything works together as one. So when thinking about linking things together, think about the changes in the text and how the way you feel changes.
This is a particularly important part of the new English Study Design where students are encouraged to focus on the text as a whole, rather than searching for techniques and commenting on each one like a shopping list.
So looking at your first paragraph – in many opinion pieces, the author attempts immediately to highlight the dichotomy (divide between two sides of the debate) by portraying himself and his ‘team’ as credible, reliable, logical and reasonable members of society. Conversely, the ‘enemy’ is usually described as extremist, ignorant, selfish, shallow or just down right weird.
So, in this particular paragraph, you could say, as a topic sentence, something like ‘Bob Walsh immediately presents readers with a disturbing depiction of the council and its supporters, likely to evoke concern and distain…” Then, go on with your ‘riff raff’ and ‘robbing blind’ portrayals.
Only thing, your essay gets better by the end. Everything reads clearer, more fluently and your last few paragraphs have a logical structure.
If you want to know what score you could get, I think this essay is in the range of 7 – 8.
All the best, for the exams!