Yeah! It is indeed short, but not to it's detriment. It feels like a distilled version of Cave Story, without the running errands back-and-forth (though even Cave Story becomes quite linear after the first couple of zones). Anyway, I got some quality time out of it, regardless of expectations.
There are some secrets!
Did you get to the replay as yellow frog with all the weapons and jetpack?
After the credits have rolled, press the shoot or jump buttons (4 presses I think was sufficient)
(I don't know if there are any special prerequisites for this to happen, such as having upgraded all the weapons or something like that)
A guy shows up (weapon salesman?) and asks if you were satisfied with the playthrough
Pick "no" and you get sent back to the beginning of the game as the yellow frog
Having all the equipment from the start gives you access to some hidden areas
Game continues after the spot where the last boss should've been
Though I have a feeling there's more that I haven't found yet.
@Ellian: iPhone is the only other format it's out on, as of yet. But you've probably found this out by yourself by now, ha.
I also hadn't realized there were newer versions of Gale! Never felt the need to check since it already did what I needed it for well enough.