On the flip side, it's better than Down and dying, or just dead.
Being "GMed" is a term we stole from HERO, referring to the point you go into long stun, as in:
Player "When do I recover from that stun?"
Chorus "When the GM says you do."
It may seem unfun but it's better than rolling up a new character, and in a system like RM, the contrast between being GMed isn't vs "You're fine" it's contrasted to "You're dead" or "You're on the ground at -120, bleeding 10/round and dying." or "You're in a coma for 1d4 weeks".
I totally get where people are coming from when they say that's just not a lot of fun, but it does make the line between fine and dead a bit more fuzzy. . .
And I'm not really sure how much more fun being -75 on the ground with a broken hip is than being -50 and stunned. . I guess it lies in the line of not being allowed to act as you want, even with a penalty. . .even broke hip can swing his sword at -75 and try, while the stunned cannot.
I've played without the restrictions on action from stun, and the result seems to actually be that high level characters and foes ignore up to a certain amount of penalty, while low levels cannot.
a -75 stun no parry, or broken leg, means the 1st level character is effectively out of the fight, barring major open ended rolling. . .the 10th level character is still quite dangerous.
Which is what it comes down to, in my opinion. . .if "Stunned" is just a -50 penalty, then it becomes casual for 20th level characters, just like a complex lock that's -50 to lockpick attempts is not going to stop a 20th level thief. . .
The fact that more often combats are between a group of 3-7 PCs vs 1 monster-of-higher-level, than vice versa, means that the PCs soon discover that they can much more afford to have a party member or two fall out of combat stunned than the solo beast can, and the scenario where in the past the beast was stunned, then the next round the beast was killed, no longer happens. . .and in fighting an un-stunnable beast to the death, usually one or more of the PCs get to join them, and go re-roll a new character.
That's not so much fun either.
It definitely affects my fighting opinions when operating solo in RM, because my tactical brain is not saying "can these guys kill me?" it's saying "All I need is for one of these punks to stun me and the rest of them will kill me while I'm stunned." . . .
When running a solo PC game, without a supporting cast of PCs or NPCs to back up the only character, I will tend to either relax the stun rules, or offer a work around so that they can survive being stunned alone. . .but with parties I tend to stick with stun, and tend not to be open to relaxing the rules or allowing casual skill based stun removal.