When it is used to do things in a way contray to what BRP was designed for.
I think BRP is able to designed to simulate the most RP situations (except toon like RP) All you have to do is to adjust the rules a little bit to the setting. Which have been done a dozen times with BRP. I have used the BRP system in SciFi, Horror and Fantasy adventures since 20 years and it worked always perfectly. Other systems I know dont do the job as well as BRP. I played
-WFRP1&2 (not very good rule design but excellent setting)
-Rolemaster, Mers (too complex)
-WoD (interesting setting but I hate the rules)
-Shadowrun (a big mistake
-Gurps (good rule design similar to BRP but too many rules)
-Midgard (a german RP which plays like a complicated mixture between AD&D and RQ. But it has IMO one of the best fantasy settings out there)
-D&D (shudder, 2 years waste of time)
Each time I returned to BRP. Its just the best and most intuitive system around. It is able to simulate everything I want from a RP and until now I found now satisfying replacement for BRP. I dont know much about some of the newer systems like feng shui or Qui. But they seems to simulate a type of "manga" style. (which I dont like)
RQ/BRP was designed around mimicing SCA combats, and as such does a reasonably decent good of mirroring such fights (perhaps too good, that is how the fumble chart got so convoluted and comical).
That was a good one.
What it wasn't designed to do was handle large scale first fights (no non lethal damage rules in RQ), or character that can throw around trucks, or keepingh track on ENDURANCE points used to power abilities. Picture grafing on HERO SYSTEMS's superpower rules over a GURPS like girrty core rules and you get a rought idea of what Super WOlrd was like. Basically, the rules were forced onto BRP and while they sort of worked, they didn't work well, or as easily as normal RQ.
Another problem is that in a super setting, character abilities can vary by quite a bit moe than in a typical fantasy setting. THis would eventually lead to situations where you skilled normal (Batman-type) character gets hit by the villian that can punch through tanks. In the comics, that sort of hit will lay the hero out cold. In Super World that sort of hit will leave the character laidd out cold-in a slab at the morgue!
Just at the fuzzy end of what BRP was made to handle. Even in regular RQ a punch from a strong character has around a 50% chance of breaking a limb. Imagine a punch from a superstrong character.
Now I know what you mean. Well then I think this is quite different to my own POV a good RP game should work. Foremost for me there should be a quite realistic world. So if Batman is hit seriously from some superduper villain you described he should be dead. Thats it. If the death of a superhero is not possible, the game would not be interesting for me. So I am more for x-men style in which the characters are sometimes dying, than for the older comic stories like superman or spiderman.