Hi just my opinion on the changes of the armor abilites.
Mobility enhance instead of Sprint: I reckon you should be able to sprint like in any other game (e.g. Battlefield 3, Crysis 2 etc.) without it being an ability. So the idea mobility enchance would increase movement speed up to 2X limited amount of time. For example, let's say you can sprint 28km/h, then mobility enhance would increase that to 56km/h for a few seconds. Mobility enhance would also increase the jump height of the user.
Armor Lock: I'll like to change the way how armor lock works by instead of having armor lock active for 5 seconds and still able to deflect unlimited amount of rockets, tanks shells during the time period, it should have a much shorter time period (maybe 1.25 seconds) long enough to block 1 rocket or a tank shell and then energy would be drained after taking the hit. However, the charge rate would be increased (comparing to Halo Reach). This would demand greater skill from the player to use.
Maximum strength: You know how spartans are suppose to possess incredible strengh as they are genetically enhanced humans. Increases melee damage (One-hit then recharge). If Halo 4 is still keeping the health bar system, then a maximum strength hit would take out the shields and half the health of the target and blowing them back but however, to even out game play, the user would take some time to recover thus making them vulnerable for a short time. So useful for finishing off a target. Also, when timed correctly, this could be used to counter an asssasination (IF brought back from Halo Reach).
Stealth/Cloak: Well I think cloak in Halo Reach was a mess up. It could be substantially improved by not jamming other peoples' and your own radar, cloak effectiveness doesn't decrease when moving but it would drain energy faster. (Similar to Crysis 2 cloak mode).
Jetpack: Should just remain the same as in Halo Reach except for the controls. It should be that you can lock the height when flying. So you would be able to fly straight when locking the height just like a Falcon(Halo Reach) instead of flying higher and higher when flying forward and pressing the armor ability button many times.