This is an interesting topic, and I agree I was disappointed, and would have happily paid more for new places in the city (like a revamped saints HQ and that stupid ship you can't enter), good activities, rescuing sr2 characters and Viola (not Zimos), interesting gameplay, no sex jokes, time travel to kill Zinyak (again) to save earth, new clothing, vehicles and customization options and having an integrated Paul fight where you actually fly inside instead of just appearing there. This sounds more like an expansion pack but gosh darn it its what I wanted! The best thing I got out of this was that since Saints HQ was in that first mission, Sandbox allowed me to place it in my map, and although you can clip inside it, it gives the city some more eye candy.
Saints Row 4 itself is something that I thoroughly enjoy, it almost definitely could be better, but theirs something about it that just... clicks with me. The character customization has so much potential, and I'm thinking of the idea of saying what your character is like, instead of all characters (it just doesn't feel right for my character) being lacking in comparison to the supposedly smart Kinsie (she really irks me). Like how smart your character is (and how they speak), your relationship with certain npcs, and how people react to you. Although I don't mind the whole psychopath who wrecks havoc thing (it works well for the gameplay no? :3).
Gat time fun time was a surprisingly great mission, in the way it helped wrap up sr3 plot lines, the awesome music, and somehow, the gameplay was just at its best in that arena and the point counter. Also fighting philipe with his new voice was awesome (why was he not a homie!?!). It gives me the idea of a reality climax editor, where you post your custom arenas and game modes on the workshop, ugh the amazement that would be.
I know volition can't do to much and this point, and I'm not sure what kind of budget limitations it has (it honestly doesn't have to do with GTA), but Titan Falls team for example isn't that big, and since the game sold so well, I don't see many limitations for the future.