I still take fun from trying to finetune a car in GTR-2 via the original MOTEC interpreter software. The sim produces a overwhelming ammount of physical data, which gets then presented and analysed in the original analysis software of the pro teams in reality are working with. Can'T say I am good at understanding all the technical stuff, but I learn a lot just from being occupied with the matter.
That is simulation, too!
Learning a complex cockpit module and realistic procedures in FS9/FSX (none of the Microsoft default airliners, but the real good stuff by PMDG, iFly, Level-D coming with hundreds of pages in their manuals) - that is simulation, too.
If you are after mission drama and battle hectic - I use to get wet sweat-soaking hands when things get
really tight in Steel Beasts Pro (and a spasm in my tongue from all the cursing and swearing

). Battle-wise, a crowded close distance battle in SBP beats everything I ever had in any other game or sim.
And then there is always the option to ignore old graphics and trying to get a copy of "Flight of the Intruder" running.