How many missions are there going to be?
75 - most of them are split between the seven gangs. (use concept drawings of the 7 gangs in gbh folder)
The main difficulty of programming an open-plan game experience like GTA2 is not the programming effects but dealing with the unexpected knock-on effects and bugs! There seem to be so many interdependencies that on one hand is what makes the game what it is - hundreds of hidden little details that only become apparent once you've played the game for weeks solid. But on the other hand it means a bug that was actually overlooked in January might only surface in May because of something else that interacts with it!
Line of sight / hearing - how does this work?
Anyone walking down the street has no awareness of anything behind them unless they make a loud noise - revving a car engine or firing a machine gun for example. However, as soon as you walk/drive in front of them you enter their "field of vision" and they'll respond accordingly - whether it's to
give chase, run, attack etc.
People are justifiably very excited by the A.I in GTA2 - a weakness in GTA has been turned into one of the strengths of GTA2. It's basically a series of small AI routines which get grouped together to operate some of the more complicated situations in the game. Above all this we have the group control which lets the police and gangs be operated as an entire unit - not a collection of individuals. One of the things Iain (Ross, programmer) is most proud of is the emergent behaviour - essentially when you a series of unexpected compound interactions - you steal someone's car in a gang area, they steal it back, but a gang member sees someone stealing your car and starts attack the car owner, which attracts the police and the gang end up killing the police - this is one of the most unpredictable, and exciting aspects of the game.