For a solo movie to be good, the main character needs to be amazing. I think Marvel in their vastness of characters, only have a few that can carry a film or series of film and have a good rogue gallery to chooses from.
I also think that if you are trying to create this universe, it makes more sense that these heroes know each other, some start working together more often.
With that being said, I generally like the team up movies more, which doesn’t have to be a large team. I like seeing these characters interact and work together to solve a problem. It is nice to see these heroes fighting together and sometimes each other, like they did in the comics.
