I want more of the galaxy I've already spent thousands of hours learning about and exploring. All of the alien species and cultures, I want to see more of Salarians and Turians and Quarians. They all have so much more potential to be expanded on in new directions.
I really want ME4 to let me play as different alien species, so I can dig deeper into the lore and alien cultures that I already have grown to love from the ME trilogy. Salarians, Turians, Krogan and Quarians are some of my favorite alien species of all sci-fi, so I'd love the opportunity to get to live in their cities and civilizations.
I never really cared about Shep to be honest. I didn't dislike Shep, but I never got emotionally married to him/her the way some people have. I always viewed Shep as just a shell that can be whatever I want and because I played so many different Sheps, it was never about Shep being "one character" but rather, just a vehicle to roleplay through.
Also, I'm sick of the reapers. They had a good run, but they got their asses kicked, I'm thoroughly done with them. I am much more interested in just seeing the ME Galaxy post-ME3 ending and seeing how all the different species are trying to rebuild. I would be totally happy with ME4 not having an ancient evil that everyone needs saved from.