[Christians] What do you believe about other denominations of christianity?

Not sure how to redpill you on it, depends on what you know already. Gnostics believe that the God of the Bible is either a malevolent or naive/misguided being who created the earth and humans to "play God", so to speak. The only way to escape this hellscape is to understand and "know" (gnosis is Greek for "knowing") the Divine Truth, sort of like enlightenment in Buddhism I suppose. To explain the entire mythology would take too much effort for my drunk self, but the "redpill" would be early church figures like Ireaneus advocating for burning/destroying all Gnostic texts. And indeed they were, it wasn't until the discovery of the Nag Hammadi library that anyone was able to know anything substantial about the actual details of the religion.

It's much more focused on personal salvation than "Christianity" is, some people think that the Gospel of John in the Bible was an attempt to bridge the gap between Gnostic and what would amount to modern day Christians. Both sects were considered "Christians" by the Romans at that point in time, they didn't give shit obviously. I would recommend looking into Valentinus, The Gospel of Truth, and the Apocryphon of John if you're looking for more info. The Gospel of Thomas is also very interesting, it was very close to actually being in the Bible and is AFAIK the only record of Jesus's actual personal teachings (obviously all this stuff is up for historical debate). It contains several things that are close to being Gnostic though, and was thus deleted.