One might think that Titanomachina has been honed to a fine edge, and while that may be the case, there is definitely some room for improvement.
There might be an issue with allowing players to avoid activating systems, particularly given how having more cards in one's hand is a distinct advantage. I'm not entirely convinced this is an issue, but I must admit that it can be irksome to know that you can reveal your entire hand to an opponent and have nothing to defend with if they're willing to play enough unactivated systems. Of course, one can work to maintain card parity with one's opponents, or simply to make them regret not activating systems.
A good rule of thumb is that you should be able to gradually increase the cards in your hand, bluff the other players to get them to waste cards, or simply knock the cards out of them with shock weaponry.
At the other end of the rule book:
The shin-kicking optional rule is an optional rule and it would be better to build in a special rule to the general rules about selecting targets within arcs, since requiring players to pay one cog to turn a Titan 45 degrees in order to enable a kick is counter-intuitive to many players, and explaining you can only kick an opposing Titan in the legs makes one wonder how to welcome an opponent to Sparta.
I think allowing leg systems, mounted to the leg stack, to count as mounted to the corresponding arm stack for the purpose of attack arcs might be a way to simplify this. They will attack like arms. Plus it opens up cross-body kicks, while requiring sponsors or turrets for back-kicks.
Mind you, the nice part about shin-kicking is, of course, being able to kick your opponent in their own legs.
Reacting to Collisions
Oh, and being able to react to collisions as if they were attacks also simplifies a special rule in the main case. Players should indeed be able to mount a defense of the flying body slam, flying elbow, and flying knee. We know what happens when the moving Titan can't force the other Titan back due to buildings in the way, and if that lands a Titan on a building.
Grappling
It works, but what if the direction isn't just 90 degrees left or right? You kind of need to catch someone napping to push them through a building, and the positioning is pretty transparent. Occasionally the deployment of a sponson may take someone from surprise, but that's again focusing on something that can be prevented with a single cog of walking. Probably good to team claws up with another weapon or sensor to be used in case of a retreating target.
But think about the things that could be done if you could pull a Titan into the hexes left or right, not just front left and front rite? Or, alternative, introduce a new weapon system that can pull Titans towards each other. I've certainly had ideas for weapons that push the attackers around (the kzinti weapon). That last one though, I think I may have a model for that.
