It's fine, but since it's an endless game, it starts feeling repetitive eventually. For me, that mark was around ~35 when I felt I'm seeing similar patterns.
Of course, it's perfectly possible to lose, but I think I could keep going for a good while if I played it safe and stayed near the centre.
From a game design perspective, endless games have to have 1) good replay value (tick), and 2) evolve over time – which I don't think this game does. And without new elements being introduced, it's a matter of time before you lose out of boredom (instead of lack of skills).
A couple of ideas:
– Over time, slowly speed up the red block, or add more of them. This is the simplest way to add increasing difficulty to the game, but it does put some upper cap on the score if you don't stop increasing since there comes a point when it isn't humanely possible to continue anymore.
It also doesn't really add anything new to the game, it just makes more challenging, but shorter.
– Add a "challenging dodge" every, let's say, 20 points; stopping all blocks from spawning for a while and spawning a scripted red block pattern – e.g. waves, or concentric circles with gaps…
Make a couple of those, at least to cover 0–200 points.
– Add a slow-moving "gold block" every once in a while which you have to pick up, otherwise you lose.
And by the way, you can have an actual scoreboard. Newgrounds has a built-in scoreboard system you can use. See API Tools in the Project System, and this:
https://bitbucket.org/newgrounds/newgrounds.io-for-unity-c/src/default/