How the roll works in Halo is overkill to be honest, but something you seem to forget here is the time it took to learn how to use it effectively... not to mention the whole time you are rolling you cannot use your weapon while you CAN still be shot.
When fighting Covenant Weaponry, yes you are fairly damn invincible; but against UNSC Weaponry you don't survive very often.
There is also the added thing where Halo Regen and Health are ALOT more agressively implimented than DUST.
I like the concept of being able to Roll or Dodge, I mean Unreal Tournament 3 implimented a double-tap direction dodge quite well without destroying any sense of balance.
In-fact what I would suggest is implimenting systems that a couple of other games have, as most games tend not to focus much on movement much; instead usually have many 1 or 2 features that are good while forgetting to impliment other really important aspects.
Cover-Based Shooting (yes I know everyone just groaned, but read) in Goldeneye Reloaded and Killzone 3 are really well implimented; where rather than being some form of "cover" button; when you got close enough to an edge you automatically used it... what makes these games better with it is they didn't take you out of 1st Person mode.
This meant you couldn't SEE what was around the corner you're hiding behind, making quick looks essencial but also a risk.
I found how they implimented this mechanic, particularly Goldeneye Reloaded (which was it's ONLY redeeming feature) was just silky smooth and inutative to use enhancing the game.
Reloading while Sprinting. This should be possible, but I think it should also have it so your view looks down slightly toward your weapon and takes a little longer... reason for this is you would need to concentrate to do this while running. This then gives people a choice of reloading and possibly not seeing someone coming towards you or waiting until you stop sprinting.
Crouch while Sprinting. This should initiate a slide, which could be used to either tackle someone or slide into a cover position... I also think if you slide while running normally you should roll forward. The reason why I think Tackle Sliding is a good idea is because if you're sprinting toward someone you generally end up stopping dead for a second to shoot back, where-as with a Tackle while the guy initating the tackle may take some damage; they both then have to get back to their feet in order to fight again. The ONLY game I've seen this really implimented in has been Tomb Raider (which it's kinda crappy) and ONI (which is good but Motoko instantly rises to her feet again).
Prone Movement. This could be initated either via the "Slide" as previously described or by holding down the Crouch button to reach the Prone state... if it's done via a slide you would be prone on your back, where-as from Standing would be on your belly.
This would make a HUGE difference as well. As "walking" in either state would allow you to inch in that given direction, where-as "running" would make you roll in that direction... pushing the opposite direction would flip you over, with belly intended as a "Sniping position" and back intended as "Close Quarters Defence". Using the "Sprint" Button if on your Belly with Forward would allow you to do a quick-burst forward, while on your back with Backward would quick-burst back.
Tapping Crouch would get you back to your feet.
That is far more inspired by Resident Evil 6, but their implimentation was just absolutely fantastic.
I think that Tapping Crouch while "Running" in a given direction should allow you to Roll in that given direction. As a form of Dodging in a way.
The final aspect that i'll suggest here is "dragging" with "Down but not out" mechanics. With the exception of a few ways you can "instapop" most of the time you remain in a semi-dead state anyway with the ability to call for help... now to me it would make sense if like Gears of War or Resident Evil 6, you were still in a semi-lucid state where you can drag your bleeding body somewhere else. During this time you're in techncially Structure so one hit, and it's game over - jump to a fresh clone. Still with this Army of Two had a good mechanic (there was an FPS with it too but forget the name) where you could drag injured team-mates when you were close enough.
Part of the issues we have right now with Logistic/Medics reviving people are dead bodies on the server are based on server physics rather than "last known position" - it would make sense with a DBNO system, that you're still there thus you're exactly where the medic expects you to be more so as you'd be able to listfully move about as well. I'm still on the fence about allowing a sideweapon to be useable in this state, but if it is then accuracy should be -50% or something making it a pain to shoot someone in that state. Perhaps even a vision that make the player seem like they're in a daze / drunk.
Logi (or anyone) can then drag them to the nearest "safe spot" (as if there is such a thing) and apply the Nanites. I think tieing the ability to give Nanites to the "Drag" mechanic would be really good on the whole.
Anywho those really all the suggestions I wanted to make, which I think would not only greatly improve the game; but also allow it to stamp a very unique playstyle.