Bruce was keen to try Osprey's new Black Ops rules again so I popped out for more gangsters action. We played two scenarios; the assassination scenario and the sabotage scenario and the key mechanic in both of them was the observation (or maybe infiltration?) rules.
Basically the rules account for various non-visible effects (e.g., darkness, fog, crowded streets). The defender is largely passive except for a few guards (whose movement is determined by die roll on a table). As things start to happen, the guards become more alert, which wakes up the defender's leader. Eventually, the defenders become fully awake and in the player's control.
This gives the attacker a lot of decisions to make (basically when to make noise). To offset the attacker's greater control during the early game, most of the defender's troops are hidden in blinds (with dummy blinds) so the attacker's knowledge of what is what is imperfect.
This mechanic is quite neat, but the rules around it are very poorly written. For example, when the attacker wants to try and reveal the content of the blind, the defender rolls. If the defender is successful, the blind stays hidden. But the rules sometimes reverse who the actor is when discussing game play (e.g., talking about the attacker being successful when they mean the defender failed the roll). The actual text is way less clear; I had to interpret some to even make clear what the problem is.
The activation mechanic is card based (each type of figure activates on a different card). What this means is that a group of figures comprising different types of troops won't activate together. This is interesting in the decisions it creates but you have to wonder how much sense it makes if you use the rules for modern combat missions.
The observation mechanic is also abstract. You can attempt to reveal a blind anywhere on the board, even if the figure doing so can't see the blind (there are penalties for this). So this means, in a skirmish game, a figure two city blocks away with no line of sight and presumably coping with streets full of people, vehicles and noise can somehow know what is in a blind (assuming the die roll is successful--or, rather, the defender's die is unsuccessful). I'm happy to go along with the abstraction but it jars a bit with the skirmish scale.
Overall, an interesting set of rules and reasonably fun to play. It is more fun to be the attacker, but that may reflect that we haven't figured out how best to play the defender. Shame the rules are not better written.