This is the Human side of the weapons that should be changed. I'll add a Covenant side if this thread stays alive. Otherwise, it would be a waste of time.
Some weapons in Halo 3 and Halo 3: ODST need a little change to them. Whether it is to give them a little more power or accuracy or if it's to take away some damage, accuracy, etc.
My first complaint is about the BR. This might upset some people, but I see Reach as an oppertunity to balance it out with the rest of the weapons.
First, take away the three shot burst and replace it with single shot (I believe it was already like this during Reach so that'd be good) so it becomes only useful at medium or longe ranges, not close range like most people are able to do with it. Then, take away the 36 magazine capacity and change it to 28 and make the maximum ammo capacity 84. It's the same amount of clips but just decreased. The scope stays.
Next, the AR. I'm sure most people saw this coming. Give it a bit more accuracy at longer ranges. Currently it's mostly a close/ barley medium range weapon. The spread on it is really big. I'm not saying change the reticule size, just decrease the spread a little bit. That's all I'd have to say about the AR.
The SMG dissapoints me. It's a close range weapon but it could do a bit more damage at medium range. Decrease the reticule size a little bit. I mean come on, SMG's today can go about 10x farther than that one and with 10x more accuracy. Don't give it a boat load more accuracy, just some.
Now the Spartan Laser. Give that monkey a destruction decrease. Take away the 5 blasts and give it 2-3. Five is a bit too much. Also, it should do a bit less damage on vehicles. Light vehicles (Warthog, Ghost, Mongoose) should be a one hit kill, but heavy vehicles (Skorpion, Wraith) should take an entire Spartan Laser to take down. I believe Spartan Lasers are just rocket launchers with a bit more range, but with less ammo and not as good against a lot of infantry (that's why 2-3 blasts only).