I have played the game a fair amount and maybe some of the concerns about weaponry can be settled, some can't, here's what I think .. also, if you've played and find something I screwed up on, forgive me, I playe d alot more single player than multiplayer, and it's different.
Some of the dual-wielding combos are absolutely horrid. I mean, it can give you more firepower, but accuracy is lower, and you can't use grenades. This makes it a little more difficult, because the problem with the lack of grenades can be a time consuming effort -- you'll see the perfect moment to drop a grenade, but you have to drop your weapon before you can throw it. By then it's too late.
The Magnum is toned down a lot, but it's still an okay weapon, especially if you pair it with something useful like a plasma weapon. The real kicker is the Battle Rifle, which is easily the new "pistol" and most player's weapon of choice. Accuracy is good, it has a good zoom feature, and it's fairly powerful as well.
The Energy Sword may pose a threat if you don't see someone coming. The lunge is not quite as long as you'd think, and I have seen more than one how it can ruin you. For example, you charge at someone planning to lunge, but they're just out of reach -- they lob a plasma grenade at you and you're doomed. The lunge aiming has to be fairly accurate, and so long as you're moving away and firing you shouldn't have any problem taking down the other person so long as they hadn't snuck up on you (or ran into you around a corner). Also, the regular melee does not kill in one hit, it actually takes 2 - 3 hits sometimes (at least it did in Campaign mode on Heroic difficult, even on Grunts - can't remember multiplayer). Also, I know in Campaign the Energy Sword will fade away after so much time, like the Overshield would in Halo. I don't remember if that applies for multiplayer.
The rocket launcher's lock-on feature: you have to keep the targeting reticle focused on the target, plus it only works on vehicles. If a vehicles goes over a bump, or behind a hill while you're targeting, you're out of luck because if it's out of sight, you lose the homing feature. It's more useful when the target is closer to you, although anyone dumb enough to charge a person who is holding a rocket launcher will probably be blown to bits anyway.
Banshees are especially in trouble against this feature, but luckily they have a way to escape -- they have barrell rolls and backflips and such, which you can perform by pressing A and the direction you want to roll/flip. This can quickly dodge an incoming rocket (if you're lucky enough to see it).
Er .. I think that was all, right? Oh, right the zoom. Yeah, there's a zoom feature on everything, I think. But the targeting reticle is no longer there, just the "border" of MC's binoculars. What I mean is, the "greyed out" area on the edge of the screen remains, but there's no way to know if you're hitting the enemy. And it's only 2x zoom. However, even though the reticle is gone, it's still really easy to pluck off a head shot, at least for me.
Anyway that's all I have to say for now, lol. Like I said, I did a lot more Campaign than multiplayer, because we only had one Xbox to play it on. Some of the rules are different in multiplayer, but from what I remember that's how it goes. Also, don't rule out the plethora of other weapons, because there's honestly more than I can remember at the moment.