Needs improvement, but good overall.
Okay. So, I like shooter games. This is a good game in terms of the story, if not a bit dry by not being more involved.
It's good that you had different levels, but did they ever increase in intensity? The fixedness of the bears kind of got boring after the first few levels, so I stopped shooting, and I still got through the levels. You should have like... a number of tourists or something that can die before your camp is eradicated.
Also, I think it would be more entertaining if you changed the background of each level corresponding to the story line. So instead of having the people defend their town, have the polar bears chasing them or something--like up a mountain, into the water (they could hide behind glaciers and underwater), and an arctic forest, with bears hiding up and popping out of every place you believe they could hide in, the value for me would go up significantly.
Music and a narrator are also good ideas--although I don't know what kind of music you could use, a strong, manly voice would be good for narration to read the news and explain what's going on at the start of a level.
If you REALLY wanted to change things, you could also make the polar bears move, although I can understand how that could take a while to animate. But starting out slow and getting faster as the storyline goes on would be great.
I hope you keep making flashes and take my advice. :)