It's a serious movie, man. Full of amazing action, but also a lot of emotion. There are lots and lots of jokes and funny moments, even in the middle of a battle but ultimately it's about saving the universe so it's a serious movie.
Totally worth watching, though. Do yourself a favour and watch it in IMAX 3D the first time, if you can. If you can't, then the highest resolution you can find.
The thing I love about Avengers:Infinity War and generally about Marvel movies is that they are not about gadgets and hi-tech suits. They are about people doing the right thing even when faced with impossible odds. Using your powers, your capabilities, whatever they may be, for more than just your own good. They are about going into a battle you have zero chance of winning because you feel it's your responsibility to give it your all even when you are staring certain death in the face.
"...because that's what heroes do!"
