BUT compared to it's rivals (RFactor, R3E, AC, PCARS) it is very expensive. With all but R3E you get everything for a small price (Never more than £50) whereas R3E has you pay for cars and tracks but they are cheaper than iRacing AND the game itself is free. I get that iRacing is a better simulation but is it really so good that you would be willing to pay the price of buying every other racing sim on the market?
iRacing sees itself with one foot in the sim/gaming world and one foot in the racing world. Compared to RF2 or AC, it is expensive. Compared to 1 or 2 track days a year in your own car, it is very reasonable. Compared to a real world 2 or 3 day racing school, it is cheap. Where I live, the cost of one track day---when you look at fees, gas, wear on brakes and tires--- is probably a year subscription plus maybe 12 pieces of content in iRacing. And that depends on how hard you push your car and how expensive the tires & brake pads are. You might be able to add another 12 cars or tracks to the mix for the same price as the track day.
You have mentioned you aren't necessarily looking for multi-player online. So... just go get RF2, AC and or GSCE. All have great strengths and also have AI. RF2 has the best FFB available and pretty much every race feature you could want including the most advanced track surface dynamics available. It is hardcore and feels alive and detailed at the limit. AC has very nice handling, a great car list-- and the list will continue to get better throughout the year if you buy the DLC and download the high quality mods. Plus they have laser scanned tracks (although they do not seem as detailed as iRacing). AC is a great leaping off point if you are coming from console-- better handling feel than console titles but still a great car selection with lots of great street cars with high quality graphics. GSCE has good FFB and a pretty unique set of tracks for a great price. And pCars may end up being a real competitor offline too-- we'll have to see how the final handling model stacks up but it certainly has some promise.
Those titles will keep you plenty busy... and satisfied... if you want offline racing. They may also give you a great online experience if you find a league that lines up with your schedule and needs.
iRacing will always be there for multiplayer if you decide offline isn't giving you everything you want. There is something unique about sitting on a grid or doing a warm up lap...waiting for the race to start with 20 other real drivers all around you on a fantastic virtual version of a real world track. It is palpably different than offline racing (which I also do quite a lot of). And iRacing's multi-player, as others have stated, is pretty terrific. They are also dedicated to continually improving things... the tire model and handling feel has gotten much, much better over the years IMO. But iRacing isn't the best at everything. It doesn't have the best FFB, or car selection but if you want challenging, very well constructed multiplayer races and want the very best tracks, then it offers value for money.
but good news is coming soon 
), I definitely have some things that I want to try on the GT3 cars in iRacing. Specifically the ABS. If it works like in real life, rather than using a formula car style modulation braking technique, I should press maximum pressure until the apex and release all at once. If there's locking, then I need to up the ABS setting. If not, lower it until I get locking and then up it one to release locking. Hopefully that should help gain time but, I'll have to test things. Otherwise, I may have to write a letter to iRacing on where there ABS system may need improvement.
