My most major concern about Halo 3 was the fact that power weapons didn't spawn when one team had picked them up in Halo 2. While looking for answers, I stumbled upon this article as well as a few more issues that are apparantly to be balanced:
http://www.1up.com/do/feature?cId=3155227
(Honestly, the whole anti-camping measures are what I'm most excited about)
Weapon Spawn System Needs a Revamp Then: Forgoing timed respawns on power weapons in favor of a control-based spawn system, Halo 2's power weapons stay in the hands of the team who grabs them, unless they empty the weapon or drop it. When the weapon is dropped, it idles and then despawns and respawns on a timer.
Fixed In Halo 3?: Tyson Green, multiplayer lead on Halo 3: "Weapon spawns have been rebuilt from the ground up." The reason the system was based simply on timers in Halo: Combat Evolved was because Bungie was still learning their way around the Xbox hardware. By the time Halo 2 was in development, Bungie could do more with the spawn system so in addition to the timers -- which sort of returned in Halo 2 -- the developers added the control-based mechanic.
While the specifics aren't locked down yet -- remember, the game is still a year away -- Bungie knows that the control-based system of Halo 2 can't remain the same. Without adding complete chaos to the model, Bungie is tinkering with adding random elements to the weapon respawning system. No, this doesn't mean that the spot you picked up an SMG will be where the Rocket Launcher appears, but instead, what if the Rocket Launcher spawned on a timer in two different places on the map? That could be a good start. What if the Rocket Launcher respawned on a timer and up to five of them could be on the map at the same time? That's a potential solution the developer is looking at with the rebuilt spawn system.
How It Could Change the Game: A level like Colossus is arguably unplayable with the current map set-up (the lone Beam Rifle at the top of the map refuses to respawn if someone is holding it). Imagine if every 90 seconds the Beam Rifle respawned either at the top of the map, or down where the Overshield currently spawns. Then, cap the amount of rifles that can be on the map at four total. Suddenly, six minutes into a match, there's four sniper rifles floating around the map and teams have to protect the weapon spawn, because if the other team grabs a beam rifle the tide can turn pretty suddenly.
http://www.1up.com/media?id=3087633 Two Guns Are Not Better, Period Then: When players spawned with an SMG, it was a mad scramble to find a secondary quickly, because if a player found someone who was dual wielding, they'd soon be watching the respawn timer.
Fixed in Halo 3?: The first step is admitting you have a problem. Bungie intended dual-wielding to be a novel, circumstantial gameplay mechanic, but it turned into the marquee: morphing Halo 2's multiplayer into a paper rock scissors pray and spray affair. The developer is setting out to fix that in Halo 3, and hoping to return dual-wielding to how they had hoped it would've been used in Halo 2.
Bungie's chief method for instigating this change is giving players a new starting weapon -- the MA5C Assault Rifle. With no zoom and no dual-wieldability, the Assault Rifle becomes (Bungie hopes) the quintessential starting weapon. They don't want players to feel powerless when the round begins (starting with a single SMG and the gimped pre-1.1 patch grenades did just that) and they want them to have a reason to seek out weapons like the Battle Rifle.
Additionally, Bungie has halved the amount of grenades players can carry. Instead of carrying four frags and four plasma grenades, now players can only carry two of each type of grenade. The catch? There's a third type of grenade now, the Spike Grenade. Still, that's a net loss of two grenades and the familiarity of how the Plasma and Frag 'nades work. The impetus behind this design choice is to keep players moving through the map -- it de-emphasizes camping, somewhat.
How It Could Change the Game: With less grenades in-hand, and more map canvassing required in order to keep those tossables stocked, Halo 3 could feel much more open than its predecessor. Couple that with a diminished emphasis on dual-wielding because of the revamped Assault Rifle and suddenly there will be times, places and situations for dual-wielding -- just the way Bungie wanted it to be.
Dude with the Yellow Bee Logo, Watch Out! Then: While the symbol-system for identifying your teammates in Halo 2 was a great upgrade over previous ones, it was also a little hard to blurt out "Look out, guy with the Ninja Turtle icon!" before someone got erased in multiplayer.
Fixed in Halo 3?: To remedy the symbol confusion, Bungie is introducing a new system for identifying players in Halo 3. Tagged "Call Signs," Bungie's Spartans will still have customizable logos, but in-game, a call sign will replace the symbol above the players' heads. What's a call sign? In the pre-alpha builds we played it was a letter followed by two numbers -- mine was L75. Not currently customizable, Bungie assured us that when the game ships next year, the call signs will be just that.
Get ready for a rush of 14-year olds using "69" in their call sign.
How It Could Change the Game: Weapon spawns and a reduced importance on dual-wielding are pretty sweeping changes, but sometimes it's the little things that count. The addition of Call Signs will make communication with your teammates
tons easier. Once we'd sorted out who everyone was (our numbers were assigned) it quickly became natural to use the call signs instead of tags.
Final Thoughts
Is Halo 3 the Halo we've been waiting for? Bungie certainly wants it to be. Is this the Halo multiplayer experience we've always wanted? If they incorporate what worked about both spawn systems, the shifting from zone to zone to protect and procure the power weapons and power-ups will return. Lower grenade counts could keep players cycling through the maps. Were these changes implemented into Halo 2 right now, there'd be an answer for what happens when teams go out into the water with both sniper rifles, two more sniper rifles would be available -- at that point, sitting in the water camping becomes a weakness, not a strength.
While we didn't include it above, the tracking on the plasma pistol has been severely reduced, while the "n00b combo" is still moderately effective, it is toned down considerably by the overall effectiveness of the retooled 32-round clip Assault Rifle.
I haven't messed around with a Rocket Launcher (hopefully the lock-on is reduced to an anti-air measure only, to counter the once-overpowered now-we-don't-know Banshees) but how the RL fares in Halo 3 will be another critical challenge that Halo 3's multiplayer faces.
There's a whole new sandbox of weapons -- the Brutes' "low brow, high tech" arsenal according to Design Lead Jaime Griesemer -- all of those will have to work within the existing context, but considering how
little of the game's undeniably robust functionality we've played, that steps like this are being taken, points strongly to Halo 3's multiplayer being the best the series has seen.
Halo 3's touch ups. 
x2
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