m50 is fine for movies but the small soundstage hurts gaming if you need to tell distance. i have a pair and while i really do like them (i use speakers for 99.9% of gaming) i realize their pitfalls. the small soundstage doesnt bother me even when i did game on them (most decent games have audio cues for forward/behind, you can tell left and right from fade and distance generally by volume) but to each their own. i liked the fact that they fold up and are bassy.
like the m50's bass but want more soundstage? look at the beyerdynamic dt770. still closed so not a huge soundstage but certainly much better than the m50. good bass, good clarity, bigger pads for more comfort.
the hd598 is a good general use can. its laid back with a fairly neutral soundstage. dont expect killer bass.. it doesnt have that. it has some but will not hit sub bass levels at all. it doesnt have crazy treble detail, instead its more mellow and easy to listen to for hours. it doesnt have a crazy huge soundstage like the ad500x but is certainly still good enough for gaming. its a good headphone if you A) do not know what you want, B) want it to do everything fairly well instead of specializing and buying multiple cans and C) if you want something that doesnt need an amp