It's a combination of things really bruh, the pain issue is very individual if a woman isn't used to being stretched both width and depth wise, some women experience a little discomfort and or pain, some feel a lot of pain to the point of tapping out sometimes. With regard to the visual that's often a big impact in its own right, again individual whether it's shock, surprise, excitement, fear or a combination of all.
Obviously a large cock is going to have the potential to fill the whole vagina at once stretching it deeper and wider than a small cock can, stimulating all parts at once.
Foreplay and warming up is essential for an inexperienced woman that's not used to a large penis along with lube etc, angle of penetration and pace are important to try and avoid too much discomfort too early and the risk of vaginal tearing.
Once all's going well I've had women cumming all over my dick that have said that they've never experienced even the slightest orgasam with their usual partner or husband, in my opinion that's what makes the biggest difference, the experience as a whole with a large penis, the anticipation, the challenge, the way it takes their breath away, giving their body a full workout, the pleasure they experience, the way they react body mind and soul, the way they're left exhausted and shattered but truly satisfied. One of the biggest changes sex with a large penis can make is on a woman's mind in my experience, the way it raises the bar, changing their expectations for what great sex should feel like and what it can do. Once the mind knows how good it was there's no way to go back to what her expectations were before, that's what truly makes the difference.