In some respects EECH
1.15.2 is still pretty arcadey; for instance, the AI's very simple and can be quite annoying (very much an if-this-then-do-that model, no cones of vision so the AI has 360-degree sensor ability at all times), the physics are variable (though it does model things like the vortex ring state, retreating blade stall, translational lift, some hot-and-high lift loss etc in 1.15.2, for instance, the pedal turns are still... strange) and the missions can be a little simplified too (very little complexity, it's always a simple "go here and do this then come home" sort of affair.
However, EECH 1.15.2 is light-years away from where the original EECH was; it does make an effort to model realistic flight dynamics (though having never actually flown a helicopter, I can't possibly make comparisons), it's introduced more realistic and subtle protection values and damage simulation, it's drastically improved the realism of sensors (bye-bye Mi-24 FLIR :() and it's done a huge amount to improve the collision detection (which was, heretofore, bloody awful).
It's still enormous fun (if at times very, very frustrating - mostly because the AI does something silly) and, I find, pretty challenging, particularly when you have the dynamics whacked up. Certainly I tend to come away from long sessions with stiff shoulders and a feeling of having concentrated hard for far too long. You can't get round some of the basic limitations of the EECH engine just yet (for instance, largely static ground units, with illogical TO&E, that sit at crossroads waiting to be shot at), but 1.15.2 really, really improves it.
However, to be perfectly honest, unless one has some reasonable stick time on whatever you're flying in a sim, I'm not sure how accurately one can assess the sim's realism!
Give it a go and see what you think. You can get EEAH and EECH from goodoldgames.com for about a tenner; hardly money to weep over