A few suggestions here:
Optional 'Reloading incomplete' message:
This was a worse problem some patches back, but still annoys from time to time.
Basically, for weapons with longer reload animations, you can interrupt the animation at a point where it (visually) seems to have completed, but the animation has not actually finished. When you cycle back to the weapon, it is still totally empty - a problem if you've suddenly got someone else sticking a gun in your face.
What I would like is the option to have a text prompt show up if you have cancelled out of a reloading animation before the weapon is registered as reloaded, so that players can know if a weapon is empty, even if it looks like the reloading animation finished.
More consistent RPG behavior:
RPG explosions don't behave consistently; they can penetrate concrete, but a few inches of dirt can stop a blast dead in it's tracks. RPGs are much less useful in 'countryside' maps like Hill 937, than they are in cities, because the rockets deal damage much less consistently in uneven terrain (e.g. crater rims), than they do in the right-angles of city buildings.
Better grenade handling:
Two issues here:
1) It always takes an very long time to throw grenade, much longer than the action would probably take in real life. By the time the grenade goes out, you are frequently either dead, or the situation has changed.
I realize that this is a tough balance issue, and I don't have a ready answer for this one. I think that the grenade throw animation should be shorter, but potentially, this could be offset with a delay in switching to / taking out the grenade (e.g. as the solder hunts around his webbing and kit for the weapon).
2) It's not always clear where grenades are going to go, or what they will bounce off of, leading to accidental teamkills. A 'ghost-image' of the first few feet of the trajectory, with indication of ricochet, would help to alleviate this.
Fix Text Chat on the Campaign screen:
Sometimes, text chat seizes up on the Campaign screen, leaving individual players unable to send messages. This is problematic if you need to, say, warn your teammates against attacking Saigon / Pleiku with low CP, etc.
A better, more feature-rich firing range and helicopter practice range:
The firing range is very bare-bones, and it is tiresome to change weapons or get different loadouts. Also, the target setup does not allow for anything other than the simplest of testing with the various weapons available.
A more fully-featured firing range would be nice. I am thinking of something like the firing range from Perfect Dark (Rare, 2000), where there are different target configurations for different types of weapons, or even mini-challenges that test player skill. This would give novice players more opportunity and more inducement to refine their skills prior to plunging into the main game.
Ditto for the helicopter range. More options and more help - especially for practicing landings - would be useful for allowing players to learn flight skills.