For me, AC is the vintage sim of my dreams. Actually, with tracks like Fonteny, it's better than my dreams.
Basically, what immerses different people is different. There's no right answer to "this is the most immersive detail" because it's up to the individual, in the same way as any subjective thing. For some it's fidelity in a tyre model nothing else matters, for some it's the realism of graphics. Nothing wrong with either.
But for me, one of the ones that gets me is the setting and location for the tracks as well as the fields. There are several games with believable vintage content but none with the quality and breadth of tracks that, in particular FatAlfie has produced.
For example, just off the top of my head, we have pre-80s versions of:
- FatAlfie (Fonteny, Thomson, Deutchlandring, Bremgarten, Battenburg ring, Feldbergring)
- Lilski (Bridgehampton, Riverside)
- Sergio Loro (Stardust, Watkins Glen, Zandvoort, Rouen, Hockenheim, Norisring, Sudschleife and many more)
- Reboot Team (Spa, Monaco, Interlagos)
- Tiago Lima (Longford)
- Terra21 et al (Le Mans, Imola)
- @Zwiss (Spielberg/Osterreichring)
- WilliamTRiker (Fuji, Nurburgring)
- Tyrone (Sebring)
- @Italotracks (Napoli)
- THL (Russelsheim, Gelsenkirchen)
- Thrashy (Lake Garnett)
- @GaryUK (Bryar)
- Jim Lloyd (Donington)
- @RMi_wood (Keimola - and countless other bits of help on others)
- Abulzz (Targa Effing Florio!)
And sorry to look the gift horses in the mouth, but so many more in the pipeline! Such as Zwiss' Crystal Palace, Italotracks' Pescara, THL's Tulln and whatever Sergio and FatAlfie may surprise us with.