It's an action adventure RPG. Open world once you get to a certain point in the game. This is the 4th game in the series though. This has been getting bad reviews because they decided to do it after the early release that was based on the first mission. Game completely opens up after that. I'm loving it.
https://en.wikipedia.org/wiki/Mass_Effect (here is the wiki for the series)
If you like games with big story-lines thats what the Mass Effect series is about, your decisions effect things later in the game etc. It's a fun series.