NIce
I seldom see 3d used in flash, and even though the graphics look dated (we're talking 1991 dated) it worked out quite well. I honestly can't say there was a part of this game I didn't like, which is really saying something because I normally frown upon Turn Based Strategies.
But there are a few things you can improve on as always.
Game-play (9/10) - Fluid, Enjoyable, and keeps you playing right to the end, as all games should.
Sound (9/10) - Very appropriate, the only thing that bothered me was the constant clanking whenever my units moved, but it wasn't a big deal.
Music (7/10) - Not a lot of options here, but it wasn't so repetitive that it ruined the game, the mute button is a plus as well.
Graphics (10/10) - Its 3d... In flash... Do you people realize how hard that is?
Options (4/10) - You didn't have an options panel to reduce the graphics for lower end computers, even though the graphics appear optimized, its still best to have options to lower them even more if needed.
Controls (10/10) - Very easy to learn, very easy to understand.
Difficulty (3/10) - Went through the entire game without losing a unit on my first run, you have no options to increase or decrease the difficulty, and after your able to get the bayonet, it becomes so easy that it starts to get boring.
Length (5/10) - I was a little disappointed at how the game ended, by the time I reached the last level I had just gotten my very last unit to max level, and I was really hoping for an extremely difficult level to show up with a new kind of monster I couldn't defeat without doing something specific for a climactic ending, but it never came.
Suggestions
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More Weapons: 6 is nice, but some are useless like the sniper, because levels are to small for it to be practical, I would suggest a few "Melee Only" weapons for some really hard ammo eating level.
More Troops: Read carefully I am not suggesting more troops per "level" however I am suggesting more troops in the menu, and the ability to select from your "barracks" who you want to use for each mission.
Custom Maps: If possible, add the ability for the player to make a custom map with his own enemies of choice, starting positions, and spawners. Objectives needn't be anymore complicated than surviving or reaching a certain point on the map.
More Monsters: The huge boss like creatures were not as difficult to deal with as I had expected when I first saw them. What about a monster that spawns more monsters of a specific type around it each turn when it moves, it could be called a "Queen" or "Hive Mother".
Options Menu: Along the lines of options I would suggest the following.
1- Show damage (add/remove the damage numbers when an enemy or character is hit)
2- Music Volume
3- Sound Volume
4- Graphics
5- Bullets (Add/remove bullet graphic when guns are shot)
6- Game Speed (Increase/decrease the speed of the games events like movement, I suggest making this accessible from the HUD as well)
That's all I have to say about this game, I did enjoy it, and spent a good 2 days playing it, great job