Excellent game. Few suggestions.
1. echoing Bubbawheat's comments, differences between characters.
2. since the game is already easy, make more challenging achievements. Like "Killed entire flying group with 9mm pistol" or something like that. Maybe some hidden ones too, like "beat entire game with 9mm pistol".
3. Faster transportation than moving platform, such as platforms you can jump down through. The game is fast, but it becomes a "run, run, wait for platform" experience.
4. More interesting/expensive upgrades like "floating cape" or something. Also maybe don't award full coin values to replayed levels, to prevent spamming rich levels.
This game has tons of promise and I've spend several hours playing already. However, especially at advanced levels, the terrible pathfinding really kills the experience. To see 30 survivors with a direct path to safety simply stumble around until they get killed by the lumbering zombies is beyond frustrating. Please please improve the pathfinding!
For a game that looks this good, it lacks a lot of polish. (1) way too much lag, especially with bosses (even the first boss, a slow beast!). (2) melee weapons are next to useless. (3) NPC melee damage doesn't match the animation - looks like you've escaped only to take damage 1 second later when ur 10ft away. (4) poor UI. Examples of the poor UI: (a) can't drag and drop to switch weapons, (b) have to "continue" after "load" (what else would I want to do?), (c) takes u to inventory screen more than once, (d) buy screens don't show what you have, (e) hard to see HP bar out of corner of eye while fighting, because it's not overlayed on the battlefield like all the other info, etc. Alas, could have been a fun game...
"low fuel" indication too late. Rest stops too random. What do lights do? Need more lanes for decision-making. Overall lacks alot of polish/balance. Good start though!
I don't care how nice the graphics are and how historically factual this is. It's a poorly executed game. A shame, but that's how it is. 2 stars. Designed seemingly for frustration and lack of information. We're not pilots, we don't know what causes a stall. Oh and if you force the laws of physics on me (stalling), be fair and force the bad guys to follow them also! I don't want a simulator; show me more clearly who the bad guys are. Just poor, poor execution.