I quite liked the atmosphere, the lack of music I actually felt is helpful to it. I also especially like the part about the lava following the player's path, feels a bit like that is the 'passage' one is creating.
I found that it was quite hard even in the first level. In like, half of my attempts I would be RIGHT NEXT to the pipe when the timer would run out and I'd just have to wait for the animation to play out, even though the time it took for the lava to reach the bug would have been plenty time for the bug to escape. It got a bit frustrating to just have to sit there.
Also oftentimes the lava wouldn't even reach the bug, it would just go a certain distance and then play the failure noise (which is a good failure noise, I have to admit. Clear. To the point. Short). Sometimes the bug could pass through the rocks as well.
Also I had to zoom out because I was playing the browser version and it's literally too tall for my screen to show it. Even though I have my taskbar to one side. This is really a game where you need to be able to see the whole game window to play it right.