Tone and attitude mean so much in written and spoken word. There is absolutely nothing wrong with being assertive, but don’t be a jerk. The “jerk” attitude may overwhelm the message one is meaning to send.
Great constructive criticism comes in three parts:
1) What worked, and why.
Often overlooked and frequently forgotten, this is important so that the creator does not inadvertently change something they were already doing correctly in the first place. When things that were working well are changed in future works, this is frustrating for the audience. It helps the creators in that it directs them down the desired path. Explaining why something does work also shows the creator why it works. If they understand the appeal, they can make it even better. It’s also not always obvious to the creator. They may have their own ideas of what worked well and what did not.
For example: even in my own worst-rated episodes, I don’t hate them from end-to-end. Usually I can find little bits of goodness in the episode that gave me a smile or a chuckle. Very rarely am I left without anything good to say at all.
2) What did not work, and why.
It’s extremely helpful to the creator to offer an explanation of why it just didn’t work for you. “It’s bad” offers no help or insight at all.
This is important because it shows the creator weak points—or as I prefer to call them, “areas of opportunity”. This are mistakes you don’t want to see the creator making in future works. The point isn’t to get them to stop. It’s to identify mistakes. As with things that do work, you also want to explain why you think it does not work. The creator may have their own ideas of what did and did not work, and your reasoning may not be clear or obvious to everyone.
It explains quite concisely what wasn’t liked, why, and it opens up a dialogue with the creator. “I felt it didn’t work because…”
3) How to fix what did not work, or offer alternatives (and why).
This helps the creator turn the problem into something positive at the next opportunity. You’re not just complaining about a problem, now—you’re showing them the problem and offering one of many possible solutions. While what’s done is done, it’s always helpful to treat the experience as something that can be learned from.
This also helps the creator understand your point of view a little more clearly. When you share your vision of a solution of what would work well for you, it helps the creator further understand where you are coming from.
The ultimate goal should be wanting to see the creator improve over time.
And this is what makes good constructive criticisms constructive.