Okay, to the original thread intent:
Weak weapons sounds. This is the number one for me. I want the guns to be loud, staccato, and believable. MW2 is okay at this. BFBC2 was a bit better except for the annoying echo. One of the best I've come accross is actually Transformers War for Cybertron (yes you should try this one). The pistol sound is perfect although probably better suited to a battle rifle. The only ones Halo got right were the sniper rifles and the Halo 1 shotgun.
I bring this up because the current SMG in IM sounds a bit... lacking. Just not as sharp as I'd hoped. On the other hand, the silenced SMG sounds perfect.
Rocket speed. From page 1 I definitely agree. Rockets need to be way faster than what you generally see out there.
Recoil on full auto in futuristic games. Okay, this bucks the trend but look at the advances we're making in the real word to cut recoil down. I don't think it's totally unreasonable to expect the trend to continue to where recoil is reduced such that full auto is actually useful. I hated how much recoil there was in BF2142. Made the feature worthless. For contemporary games like MW2, BFBC2, yeah recoil is fine. But it is a little less fun. And in the IM future, why not?
Inaccurate weapons for the sake of balancing. MW2 is the worst offender here. Guns are nowhere close to there real-world counterparts. The medium machine guns are weaker than ARs. Ever see anyone shrug off a couple hits from a real M240? Me neither. Strangely Halo is also pretty bad at this. Assault rifles should be assault rifles, not glorified SMG's.
Well that's all I can think of at the moment. Oh yeah, and lack of giant walking land sharks. That really bugs me about most of the shooters you see out there today.