Man, Fire Fighter games are extremely underrated, double so for well made ones such as this.
The difficulty is a bit unforgiving, mainly with the pacing of Rescuing everyone trapped inside and then racing to save the building afterwards. I rarely got through a level on the first try. Once I got a bit more familiar with the level layout it became easier to manage since I could clear the areas I needed cleared more quickly.
I love the idea of the foam mechanic to create safe zones. However there is a bit of an issue is just how limited it is, either using it to make a fire proof zone, or to blitz through an area quickly and then your out after using it in 2 situations. Then there is the smouldering walls and ceilings, nothing brought me more frustration as I'm trying to put the last fires out, and the smouldering walls re-ignite the areas I cleared and I lose the game solely because of this. Plus there's no way to fully put them out without foam.. when I used up all my foam for damage control earlier on.
I tried spraying them down with the water sprayer, and it sounded like it worked, but it didn't do anything. I don't know if this is bugged or not implemented yet, but I'd recommend at least making it so the Water Sprayer turns any smouldering surfaces from "red" to black, but they'll reignite if another flame source goes near them.
--My Recommendations--
As much as I wanna say the player needs a tad more foam (maybe like an extra second or two) so they have more margin for error, perhaps it might not be needed depending on how the difficulty is adjusted later on.
There needs to be a way to permanently extinguish smouldering walls/ceilings without foam. Since they are usually a massive annoyance at the end when trying to douse the last few fires.
Also there needs to be some elaboration on not to break open windows. Or at least I assume breaking windows is bad because it allows the fire to breath more easily and thus spread.
Never the less, the challenge still makes this game exhilarating and satisfying when everything goes to plan. Mostly just needs some polish and I'd say this is going in a great direction.