My main worry going into Smash 4 will be about characters that have already been in Smash Bros. I obviously want Mewtwo and Roy to return. However, from Sakurai's statements about Brawl hitting the limit in terms of what's feasible, I do have a worry that Sakurai will go become "axe happy" with Smash 4. Some of the newcomer characters for Brawl that I really liked/wanted to be included such as Diddy Kong, King Dedede, Wario, Meta Knight, Pit, and Olimar are safe. However, Brawl characters that I liked that I am worried about are Pokemon Trainer (with Squirtle, Ivysaur, and Charizard), Sonic, Wolf, ROB, and Lucas. I am also worried about possibly Jigglypuff and Falco being cut. Overall, I will be very different than most Smash Bros. fans going into Smash 4 (assuming Ridley and Mega Man are among the first characters announced). Unlike most Smash Bros. fans that are active with speculation, most of my character concerns will be with characters returning.
Overall, Brawl's roster was only a few characters away from being "perfect" to me.