Here's some information for you to print and bring to your vet--there are three pieces to treatment that are very important in treating feline diabetes successfully. Diet, home testing, and the right insulin.
AAHA diabetes guidelines
And I've attached a more detailed article about treatment below. I would print both of these out to bring in. Many vets are good vets and just don't have up to date information on feline diabetes, and the research that supports the change in treatment didn't come out until 2009. Cats are now treated very differently than dogs, and recent research has shown that with correct diet (low carb canned food), home testing, and insulin (Lantus or Levemir), most cats will go into remission and no longer need insulin.
Novolin N is good for dogs, but it's not a good insulin for cats. It's hard to regulate a cat on it and it has dangerous drops. Many vets prescribe it because it is low cost, and the better insulins for cats are pricy in the US. However, many of us order them from Canada, which actually makes them more cost effective than the cheaper insulins, and they are much more effective in controlling diabetes in cats. After you change the diet and start home testing, if the Novolin N isn't working well in controlling his diabetes within 4 weeks, I would strongly recommend you try a different insulin that is recommended for cats.
A word of warning--if he's eating dry or high carb food,
please do not change the diet until you are home testing! Most cats see a 100-300 drop in blood sugar once the diet has been changed, and the insulin need reduced.
And I can attest, home testing gets much easier as you and your cat get used to it. Bandit fought me tooth and claw when we first started, and I was in tears. But we gave a treat after every test, and now he comes running when he hears the meter beep on, and sits and purrs through the whole test. The pokes don't hurt them--cats have less nerve endings in their ears than people do in their fingers. They just don't like that you're nervous and doing something new to them.
I wish you the best of luck! Diabetes is very treatable in cats, if you focus on points of treatment that have been proven to be successful.

Bandit has been diabetic for over 7 years, and we've not needed insulin for most of that time, thanks to the advice here on FDMB.