Just on the alien rising (in water?), I suspect it's just the editing that has it appearing to be in the same scene as Daniels in the suit, that water is being affected by gravity, she's clearly not in gravity :-)
But on the alien itself - excellent. And I bet you that's a completely practical alien head. The set visit articles made clear the amount of effort that has gone in to practical effects, supplemented of course with CGI. THAT looks practical to me, and is exactly the shot they would use it for.