A lot of the film is in English as they speak it but the Korean bits are subtitled. This is fine although I would hedge a bet and say those who speak 2 languages fluently will appreciate the original language with subs more because of the nuance aspect of native languages!
Watched it last night, I enjoyed it and it has a nice aesthetic/special effects
With regards to the subtitles, most of the main character dialogue is dubbed into English but there are other side characters who are subtitled as they are speaking other languages (French German etc).
As someone else said, its a good film not a fantastic film but worth a watch if the trailer interests you.
Watched it this morning, definitely take brain out and enjoy the visuals, the cast didn't work out too well and not sure if it's a Korean thing to have a 'hard ass' female Captain who looked like trying to a edgy popstar. CGI was well done and puts lots of western stuff to shame.