Eh, lets face it
This had a lot of major shortcomings. A lot of things could use more detail and the thing was a bit choppy. Despite this however, it was still reasonably well done and theres nothing you can't fix for your next one. Here are a few ideas for you.
1. Increase the frame per second rate. It looked a bit choppy so I'm guessing fps was the issue. Try something around 26fps.
2. Put a bit more detail into the set and stuff. Granted this is a movie of d-day with friggen video game characters, but try to make the backgrounds look a bit better.
3. Think more about where you use the line tool. It can be useful for helping something take better shape and then deleting the line.
4. Try different shades of colors. Everything seemed like it was either grey, green, brown or something like that. Try to make it look like theres actual lighting effects or something by making parts brighter then others. Makes things look less 2d.
Thats all the good advice I can really think of. Good luck on the next part!