Nothing. Those that say otherwise haven't the slightest idea how to play him. And for once I'm being serious about that statement, not trying to troll or be a douche, but the Human engineer is perfectly balanced and quite flexible. The Combat Drone can be a bit iffy at times, but a lot of it has to do with how it rarely get's any attention until long after the enemies have gotten a hefty buff, but it does still make for a quick distraction and it's saved my ass a number of times by either pulling aggro or getting in that last needed shot at the last second. Overload makes quick work of of shields and synthetics and drops the low tier enemies if you spec for it, plus the tech bursts you can make. Incinerate helps with armor, setting off fire explosions and even causes some of the enemies to panic, making them easy pickings. If anything my only complaint is finding a good weapon to give him during gold and platinum games that still let me have a minimum of 180% cooldown so that while I'm waiting to use my powers again I can keep killing.
If his Combat Drone could be switched out for a Grenade, he would be even better. Otherwise Human Engineer is one of my favorite classes to play since he is well balanced against all enemies. --- Xbox 360 GT: o 8bitPunk o
Very good character. Can be dropped easily, but combat roll is a great dodge (my personal favourite) and can be used to survive quite well. Overload is amazing and synergizes well with Incinerate, allowing back-to-back Tech Bursts and Fire Explosions. Combat Drone is useful for distracting enemies as well, adding to the class's overall survivability. --- Gears of Halo 4: Black Ops II