Some things that I think will make everyone happy (campaign and multiplayer) while keeping the game balanced:
1. Remove the energy drain from power kick/melee interaction with objects. It already takes a while to charge the kick and you can't really do it without coming out of stealth.
2. Make "Air Stomp" a default ability that doesn't drain energy. It takes timing and the right situation to do it, not to mention that after you do it, you are frozen in place and unable to do anything for a couple seconds. Even if you stealth right away you are frozen in place and anyone could guess where to shoot. Armor would probably mean certain death as well, but at least you can sprint or jump away.
Just a couple things I think could make the game better overall.