If this game has more of a linear storyline and people are simply completing it, then the playtime as an issue. Portal is a great game, and you likely won’t spend 100 hours in it.
It looked like it was an open-world explore/build game, which normally means a long playtime of self-directed goals. If you can’t keep your players engaged for 100+ hours in those types of games, then the world or the mechanics aren’t engaging.