With new games I find myself getting sucked in and being massively entertained up until about halfway through, at which point interest suddenly dwindles down to nothing for some reason. There are, of course, exceptions to this. The Mass Effect trilogy kept me bolted to my PC from beginning to end, but that kind of thing is more and more rare.
I grew up in the age of Final Fantasy 3, Breath of Fire, and Chrono Trigger. Games like these drew you in stat to finish, and kept you coming back for more. Chrono Trigger is still my all time favorite game EVER, and I own it in every form it's been released, SNES, Playstation, and the DS Remake.
However, I think a part of the difference is availability and "freshness" of things. Back in 1995 when Chrono Trigger was released it was one of the largest RPG's made, and featured multiple endings based on how you completed the game. The Final Fantasy and Breath of Fire series were in their infancy, introducing features that continue to be used to this very day. But these days things aren't really ever AS new as they were back then. It's getting harder and harder for games to continue to blow us away with a slew of new features, and a lot of it now boils down to visual presentation as opposed to actual content.
As for me, when I play a game I guess somehow I'm always comparing it to the past epics, and a lot of the time I find new games to be sorely lacking. I mean I can think of dozens of oldschool games that were, and are still, absolutely fantastic. I regularly play a lot of the older RPG's to this very day, and enjoy them as much or more than the newest games being made. But still every so often a new game will come out that I find truly impressive and innovative. Games like the Mass Effect series, Borderlands and Prototype, that introduce loads of features and game play that we haven't really seen before. I just wish it happened a lot more often.