Personally, I would aim to make Halo 4 more like the classic Halo's (1, 2, and 3). 343 has brought back the BR and have done away with bloom, which is a great start, but I would like to see a few other changes made as well.
First, the removal of Armor Abilities. AA's give the game an abnormal flow while playing, and they take away the traditional feel of Halo. Even the equipment changed this to a certain extent. Before these things came into play, it was just you, the accuracy of your shots, and your ability to evade enemy fire. AA's and Equipment made things easy for the player though, instead of having epic battles for power ups, you have people wearing an armor ability that makes them invisible. Instead of having to shoot a gunner/driver out of a vehicle, you can simply power drain or trip mine them. Instead of having to run away strategically when you're about to die you can simply armor lock, bubble shield, or sprint away etc. etc. Even the jetpack is pointless, you're super easy to kill while flying, people flying around the map changes how Halo's gameplay should feel (ground combat), and not to mention you can get to areas on the maps that shouldn't be accessible. An easy fix for all of these things would be to have two sets of ALL of the playlists, one with AA's and equipment, the other obviously without them. This would give the players a choice between what to play based on their own views.
Second, and probably the most important change for me would be dedicated servers. Dedicated servers are going to be expensive, but when you compare the cost to the satisfaction of millions of players, it's extremely worth it. I can't tell you how many times I've been in a matchmade game where the connection drops to red bar and everyone starts lagging because the host has a bad connection. These servers would be hosting the games as opposed to people around the world with varied connections thus providing us, the players, with a stable and consistent connection.
In summary, I just want the classic feel back, battling strictly for power weapons, camo, and overshield. All of the additions have slowed the game down and have made the target audience people playing strictly for fun. Personally, I play for competiton so faster gameplay and challenges are what I'm looking for.