Rotten Tomatoes finally released its score on Justice League which sits at 40% favourable. And having read some of what they deem “favourable”, a nonbiased source would probably have it closer to 20%.
In comparison to the Justice League hyperinflated 40%, Iron Man 2 is at 73%, Iron Man 3 is at 79%,
Thor 1 is at 77%, Thor 2 is 66%, Avengers 2 is 75%, the two Hulk movies are at 61% and 68%, the original Spider-Man trilogy are at 89%, 94% and 63% and the followup duology are at 73% and 52% while the most recent one is at 92%. Meaning the majority of critics liked all of the Marvel movies you mentioned even the second Garfield Spider-Man movie, while that is not true of the DCCU movies with BVS at 27%, Suicide Squad at 26% and Justice League at 40% (Man of Steel is at 55% which I consider surprising although I admit I like it better than the other DCCU movies excluding the actually decent WW)
But the WORST rated MCU movie is the second Thor (as the First Hulk wasn’t in MCU) is rated at 66%. Which is not surprising, I liked Thor 2 but there are enough bad moments (basically everything with the now dropped Natalie Portman) I could see where every third person might find the bad parts overriding the good parts. Conversely, I can’t believe a fourth of critics could even tolerate Suicide Squad and BVS, those were complete garbage almost to the point they are such garbage it becomes enjoyable to make fun of it (I will admit, while BVS is terrible, the dubbed TLDR version by HISHE was hilarious so I’ll post it below).
PS If you want to really bag on Marvel (although not the MCU) you should mention GhostRider. Those are truly DCCU terrible and their RTS scores reflect it.