Warframe.

Before they streamlined the prologue section the game had very little clarification in terms of setting and context.

Kept trying and putting it down a few times because a friend insisted it got better.

Then once I made it through the prologue it started to click and I've put in close to 10k hours since. Been playing for more than 10 years now.

I play it in bursts. Maybe 3 months a year. Keeps it fresh every time I play it.