I had a lot of fun with this game. The art style is cute. The music was pleasant, and despite being a relatively short loop, didn't get repetitive for me in the ~20 minutes I played. I thought it was a nice bit of design that you need to go fast in order to break through a gold block, which makes you more vulnerable to upcoming grey blocks.
I found the spawning algorithm to be a bit hit or miss, some games it felt like long lines of gold blocks were frequent, whereas in others it felt like 5 or 6 grey block groups would go by before a single gold block would show up. It also felt like it was a bit too easy to crash into a gold block next to the one I just broke through when exiting dive mode, usually to avoid a group of grey blocks directly below - could use a bit of tuning. Finally, there was one game where I destroyed a gold block, but came out of the dive early enough that I also crashed into it simultaneously, which felt a bit bad.
Overall I thought this game was great - simple but addictive. Nice job :)