So, there's a lot to talk about here. First of all, the game has no save. This wouldn't be such a bad thing for a quick-and-dirty little gadget game, but in this game so much time is needed to unlock upgrades like the second car that the loss of your save data at that point is a catastrophe. That brings me to the second major concern, and that is just how long it takes to save up money. The first mission starts with 16 seconds of waiting for the first enemy to show up, then another 29 or so seconds for the second and third enemies to arrive. That may not seem like a long wait, but after the 20th or 30th run it becomes unbearable. You will become keenly familiar with the first 2000m of the first mission as you will have to run it (with varying levels of success) over and over, making little bits of progress each time.
Another issue is the music and sound. The music was fine at first, but unless I'm mistaken there are only two songs, the garage theme and the song that runs from the beginning of the game all the way to the final boss at the end of mission 3. The sound effects can be wildly different, with the starting minigun and the plasma truck's laser weapon being nearly silent... to the weirdly loud and annoying plasma gun "pew pew"s.
If you're really interested in this game and think it looks like fun, I recommend turning off the audio, pulling up a podcast or some music and just running it over and over. I also recommend at least a few runs just pointing your gunfire at the right side of the screen and leaving the game to run. You won't make it nearly as far, but at least it's some amount of currency you can obtain while you're in the bathroom or dusting your house or something.
IF YOU ARE USING CHROME, look up how to turn off auto-reloading of tabs. Not only is that something that has long bothered me, but in this game in particular it makes it nearly unplayable with the lack of a save.