I love iRacing for its amazingly detailed tracks and cars, and the fact that it is currently my absolute favorite racing sim for providing what I consider to be a realistic racing car feel.
I hate iRacing for, well, online racing. To be fair, that's what iRacing is all about, but I find something like Project Cars to be a better choice for me when it comes to head-to-head racing. I don't have to wait for the scheduled race time to come around, I can simply restart when I inevitably wreck, and when that wreck was caused by me, no one gets angry.
iRacing to me has always been about hotlapping. I would engage in multiplayer private sessions with realworld friends, and enjoy it greatly, but when it's convenient to sit down to drive a few laps without having to make arrangements or appointments, iRacing solo is, or was, the best choice.
iRacing has changed all of that with the new Time Attack racing mode. The one thing that had always been lacking in my solo driving was a measure of how well I was doing it. It's very common for me to think I'm killing it in practice, only to enter a race and get left at the back of the field. Time Attack actually adds a competitive factor to solo driving.
The folks at iRacing can describe it better than I can:
Time Attack is a single car, hot lapping competition that ranks your fastest lap times against those of other iRacers in selected official series without regard to license levels, iRatings or Safety Ratings. Your single fastest laps for each track in the series will be added up and, based on how your total elapsed time compares with other members, you will be ranked from novice and challenger all the way to expert, pro and - finally - world champion.