racer.com has a rah-rah article about iRacing.
http://www.racer.com/console-racers-help-fuel-iracing-growth/article/309997/#
"With road racing and ovals, stock cars, sports cars, open-wheel cars, touring cars, and production cars, iRacing is really like dozens of games in one. "
And priced like a dozen games (if you buy all the tracks and cars you need for the higher race series). I think that many pc sims are a step up in realism compared to consoles and sims like rFactor2 and Assetto Corsa may be better than iRacing at least with the last tire model. The new tire model puts iRacing on pretty close footing to rF2 and AC. It's currently only on four cars but should be phased in for all cars over the next couple of builds.
The three major selling points for me are:
1. The laser scanned tracks. iRacing tracks are second to none. They scan the tracks in higher detail than AC and others. I think it makes a huge difference in how the tracks feel.
2. Performance. While iRacing uses older graphical technology, it still looks pretty good and performs exceptionally smoothly even with triple screens on my system.
3. Most important to me is the racing organization. iRating makes it more likely that you are racing against similarly skilled racers. Safety rating encourages cleaner races. The race scheduling means that I can always find racing when I have time and I can even take part in a points racing series.
The game can be too serious if you let it. The key for me which made things a lot more fun was finding races where I didn't need to worry so much about iRating or Safety Rating. That used to be the rookie oval series for me but has now moved to the Carburetor cup (a Nascar race with no effect on iRating or SR) and hopefully the Indy oval series.
On another note, several of the GT Academy finalists are primarily iRacers.