XCOM: Enemy Unknown. There's another thread going right now about how awesome it is, and I agree with everything there, but for some reason I just didn't have the stamina to finish it. I think it is because I couldn't see an end in sight. Things kept unfolding and the stakes kept rising but it felt like all I was doing was reacting instead of strategizing.

I have hundreds of hours in X-Com Enemy Unknown and X-Com 2, with probably 4 play throughs each.

I have actually finished the last mission once in EU and once in 2. The game to me is leveling up your dudes. Once you're maxed out and/or on the last missions where there's going to be no more powering up, I just can't be bothered.