It's a decent, cute little game, but I felt like the tunnel trip got old quickly due to the simple flying controls and lack of challenge and variety in obstacles to contend with.
Once I got one bat to the end (which I did on my 2nd try easily) I didn't really have the willpower or inclination to go through it again as the game expects you to since 1) the track just goes on and on and gets boring since it caps out on difficulty early and doesn't throw in any new exciting obstacles 2) the upgrades don't really add anything new or exciting that would make further trips down the tunnel feel fresh (likely it would just make it feel easier which would just make it even more boring) and 3) it didn't seem like there was a clear end goal to reach, making me feel like it would just go on forever with no ending and feel pointless.
It's an ok core gameplay at its heart that could be nice with some further development: at the moment though it's just too simple to justify the amount of grind and commitment it expects. Perhaps you should need to get a set number of bats through with each subsequent set having different control schemes (maybe one of them having a flappy bird-esque movement pattern), perhaps the tunnel could change and there could be other obstacles and new power-ups to try and help combat those, and so on.
Oh and also I feel like the bat should probably be on the left side of the screen, instead of the center, to make it more fair and give you time to see obstacles coming from the right. That is, unless perhaps later on you make certain obstacles fly in from the left: that would justify it and add some variety!