Well, to stay interested in it I think you need to definitely get a few seasons in like someone said earlier. When you start off you don't know any of the players, coaches, etc. I'd say in the three fictional leagues I've played (currently in season 6 in one and season 14 in another, did 9 in one that I stopped) it usually takes to about year 3 or 4 before you start really getting engrossed. By then you know who the star players are, the draft starts to shape up and free agency comes into play if you reset all their service times to 0 when you start (which I do).
For example, in my Year 14 league I'm really engrossed because numerous story lines seem to play out every year, like players going to rivals in free agency, retired players becoming coaches and leading teams to the championship, I change the names of draft picks so some 'sons' of players who have retired are now coming into the league, etc. Next year, year 15, the Hall of Fame will finally begin so that's a new wrinkle I'm looking forward to, and I'm having my first league expansion of 2 teams. I'm excited to see who will be made available for the expansion draft and how the new teams do.
Now, I've been in control of one franchise for all 14 seasons but I don't make ridiculous trades to win every year. I keep everything as realistic as possible. In my second phase of expansion in a few years I'm going to leave and take over a new team for a new challenge to start from the bottom.
I am also obsessed to the point I have about 5 or 6 different types of spreadsheets tracking milestones, best players for each franchise, etc. that keeps me involved.
