More variants of weapons already present would be best, in my opinion. I like the idea of the AK-47, as it gives Commando some much-needed strength. Maybe a bolt action sniper rifle could be a viable alternative to the crossbow? It would have higher damage than the crossbow, but would only penetrate one enemy and have a slightly higher rate of fire. This way, the crossbow would be more useful against large groups, but the sniper rifle would be more suited to big, powerful enemies like fleshies and skrakes.
For a new melee weapon, you would really need something with a long reach. A halberd actually isn't a bad idea, although a claymore might be a little more badass. It would need higher damage than the axe with a much slower attack speed, and the capability of hitting more than one enemy with a swing if it dismembers something. If you don't dismember, you shouldn't be able to swing through. A sledgehammer would be fun, as someone said earlier in the thread. A bit longer than the fire axe, more damage, slower, but you get to smash heads.
New handguns? Sure. Why not? I wouldn't mind a Colt .45 for a balance between the power of the handcannon and the magazine capacity of the M9. A USP would be fine, too, but Colts are more stylish.
Firebugs are kinda left out, in my opinion. Perhaps instead of making their grenades catch enemies on fire, they could get molotov cocktails. Gotta pick firebug to get molotovs, and they replace their grenades. You get it at the same time as your grenades would catch enemies on fire. They would simply be grenades that didn't explode as violently, but they would burn in the area for a while (say 30 seconds). This way, a firebug could be incredibly vital to the survival of a team because they can shut off a narrow hallway with a molotov or two. I see how this could be exploited, but then again if you get 5 guys standing in a hallway with shotguns then that amounts to the same thing.
Speaking of shotguns, why not introduce slugs? Add another ammo type to the pump shotgun, making it more useful later in the game. Where you would have "fill ammo," simply add another button and make them "fill ammo (shot)" and "fill ammo (slugs)." You wouldn't get the spread, but you'd have a lot of power to throw at one target at a time.
Since I'm kind of on a roll here, throwing out something for every class, why don't the medics get any kind of special weapon? They get a movement speed bonus and improved armor. Ok? You still have to kill things. People seem to like the idea of SMGs, so why not give medics a damage boost and discount on a couple of new SMGs? An Uzi and UMP would be sufficient to start with, giving you a high rate of fire with a 9mm Uzi (or TMP, or MP5, or whatever else you wanted, there are tons of 9mm SMGs), and then a lower rate of fire with the more powerful .45 caliber UMP. This would give medics a fun toy to play around with, instead of just having the ability to run away and heal people.
In summary:
Bolt action rifle w/ scope to compete with crossbow.
- Less penetration, higher damage, slightly higher rate of fire
Claymore/Sledgehammer/Halberd
- Longer reach than the fire axe, possible to hit multiple enemies, slow attack speed, high damage
Shotgun slugs
- Higher damage, no spread
Handguns! More of them!
- Colt .45 or USP, I don't care, they're both fun.
AK-47 is already being done
- Higher power, lower rate of fire than the Bullpup, heavier probably
Medic SMGs
- A high-rate, low damage 9mm SMG, and a low-rate, high damage SMG, with Medics getting discounts on price, and damage bonuses or something
Molotov cocktails
- Replaces grenades for Firebugs, burns in an area for a short time, can be used to block hallways where doors have been broken
More weapons is always a good thing.