I really liked your game! I failed both of my attempts (i got 31%- so close!).
This game should be an example of how to do a game that's simple but very effective. But let's go through all the parts :)
Gameplay. Once I saw where the fire station and hospital is the gameplay mechanics became instantly clear. One thing- I think I failed my first run, because I figured that the ambulances must return to the hospital. But I guess that's on me :) It was cool, that I could assign multiple cars to one event (it's not explained in the instructions, but I tried it, it worked, and I was happy). The game is fast and a bit difficult, but in a fair way. The city is designed in an interesting way. Sometimes it was more beneficial to reroute a car that was already in the city than send one from the base, which made me feel like I was thinking on my feet. Bugs? I guess sometimes a car stopped in the middle of the city, and once the ambulance parked in the fire station. Nothing game breaking, barely noticeable really.
Graphics and audio. Graphics were much like the gameplay. Seemingly simple, but very clear. In the game, where you need to cover this much ground you need to know what's going on at all times. And thanks to clear graphics, icons, and the call sound I was aware at all times. One thing I'd add is some sound when the car ended (or failed) a mission. Again- not really a problem, more of a nitpick on my part :)
Use of the theme? I'll be honest here- I think making a game about saving lives under the time pressure is the absolute best way to interpret this theme. That's why I made a game like that :)
Over all- I had a brilliant time playing your game! Keep it up!