I'm not much of a Suppressor user, but I think it has fantastic advantages in gametypes like Oddball, CTF and KoTH. If you have a Jetpack, the ability to rain Suppressor shots down on your enemies is a massive advantage. I've killed many a ball carrier by raining Suppressor shots down on his head. At close range, it's a monster. You can mow through 2-3 enemies before they can even respawn in a CQC area, and then destroy the Flag Carrier/Ball Carrier (or clear the entire hill). The Suppressor, despite being a "Spray and Pray" weapon, is a powerhouse in objective modes, and should be treated as such.
The Storm Rifle is much more useful than I used to think. It's mid-range accuracy makes it a much better choice than the AR, despite it's CQC limitations. I'm starting to use it more and more, because even though I'm used to the AR, any noob with a DMR can put me down before I kill him. The Storm Rifle shakes up their shots enough to give you increased survivability.
The AR is somewhat of a compromise, lacking the mid-range kill speed of the Storm Rifle and the mowing capability of the Suppressor, but that doesn't make it useless. Playing in a class with Mobility, Dexterity, and a Jetpack, an AR user can rack up multiple killing sprees with an AR. I would know, I've done it before. The AR is still not my favorite automatic weapon, but it's good enough that I use it regularly.
What I think is being missed in this entire thread is a look at the power weapons. The Needler is a monster (as it should be) and doesn't need to be changed now (besides maybe slightly faster needles). The Railgun's charge is a counter for it's 1-hit kill capability, but the time it takes to hit a target over any distance and the massive bullet drop makes it a mid-short range weapon, when it could be a long-range killer too. The slug speed and bullet drop need to be fixed. The Concussion Rifle was toned back a bit, which is good, but it's instant stopping capability is ridiculous. Significant slowdown would make sense, but not instant freezing. That causes concussion-lock and pisses off gamers. The Shotgun and Scattershot have no flaws (besides the Scattershot's BS bullet spread) and the snipers and heavy weapons seem pretty well-balanced (besides some small issues with the SR's massive recoil when you get shot and how slowly it shoots) but the Spartan Laser pisses me off. 4 shots? Really? 4 shots is not enough. Halo 3 had it right with 5. 5 works the best. The sword lunge has some BS lock-on (it sometimes doesn't when it should) and coming out of a sprint with that thing will usually get you killed. The Gravity Hammer, on the other hand, has too small of an insta-kill radius, but too much range. That should get fixed.
That ends my rant. I've commented on secondaries and precision weapons before, so I'm just leaving those out.