Realistic controls that takes time to get used to, but full of awesomeness once you mastered the controls.
You need to use every button on the num-pad to control your mech, or gear. Compared with other mech games you will notice that the controls in HG2 are much more "manual" than other games, but in a good way. What you will miss is the auto torso turning and auto aiming. What you gain is the ability to shoot without stopping and the ability to predict where the enemy will be and aim there instead.
In space the controls simply makes sense. You are required to manually use the thrusters on your gear to get it to do what you want. What you will miss is the ability to always keep enemies at sight range (lossing sight of the enemy happens very often). What you gain is the ability to do almost whatever you want in space.
Another aspect of this game is the damage. When the enemy hits you in specific spots you either takes extra damage or receives negative status such as losing your weapon(s). You can apply the same status to your enemies as well. While these status are annoying sometimes it also makes the game much more realistic (in other games your mech might get stronger and faster as you are dying). The downside though is that there is no repair kits available, so when you get a status sometimes it means game over (e.g. when your torso is damaged you cannot aim left and right). This is one big aspect of this game that is missing. That is the reason why I gave this game 9 instead of a 10.
Overall the game is very revolutionary and very fun to play. Some battles I had were amazing. The only complain I have about the game play is that lack of space battles. Only 4 out of the 22 missions take place in space, and 2 of them doesn't really count.
The control does take a while to get used to, specially in space. But once you mastered the controls the game is a blast. I would recommend any mech fans to try this game out.