p.s.: my worry is that it will not play
these are my specs
https://forums.macrumors.com/showthread.php?p=17083147#post17083147
people tell me it won't run or even have trouble on low ?
ps 2 : is there a demo ?
That's because your iMac has a very weak graphics card. The 9400M you mention is also pretty poor (it is NVIDIA's equivalent of the Intel HD 3000 integrated graphics, but older). It might run, but only on low settings and nobody can make any promises about performance.