Almost anyone you talk to about this game will almost certainly start talking about it's name at some point, and I am no exception. "Shooter" isn't a particularly good name for this game, but it's not like a better one immediately springs out. Q-Games obviously thought the same as they put it to the community to name their game, who did it about as well as you would expect. They call it "1-4" at the bottom of the screen, which doesn't work for me because even as I type this I am thinking of jumping over Bowser and hitting the axe thing to kill Bowser.
This game is certainly about fluids and fluid dynamics, but there are also gasses in their so you can't call it "Fluids". "Elements" makes it sound like photoshop or that terrible Might and Magic game. Personally it sort of reminds me of descent in 2d, so Pixeljunk Descent would be alright. Doesn't have escaping from reactors though.
4 paragraphs in, I realise that I should probably talk about the game. So it's a 2d side on game, left stick controls movement, right stick controls which direction you face, but doesn't fire anything so it's not technically a twin-stick shooter, you have to press a button to do that! You fly through caves saving dudes, and messing around with various materials like water, ice, explosive gas, and weird magnetic iron filings. These all interact in interesting ways and are what make up the majority of the puzzle element of the game. Water turns lava into rock which can be shot, ice freezes water, lava ignites gas, etc. Messing up in this game and you'll end up with an enormous wave of lava rushing through a hole and killing you instantly, which is actually a lot of fun in itself, and provokes a real "OH GOD!" reaction as your tiny ship is swept away.
Health is heat, be too close to heat and you overheat because of the heat and die. Stay in water and you cool of and basically become invisible. There are some enemies that'll shoot stuff at you, and getting shot is a good way to increase your heat, so don't do that. There are 3 stages of 5 missions which consist of about 5-7 screens. If you do the math that's urr between 75 and 105 screens? Maths. It's not super long anyway, could probably get through it in 5-6 hours. Though if you neglect collecting enough crystal things you might have to replay a few, and if you want to get all the crystal things that'll probably take you a while.