I think I managed to fly the Dodo all the way to the western edge of Staunton Island before flipping it over in mid-air and crashing into the street below. I'm sure part of the reason they made it so difficult to fly was to keep people from flying out of the boundaries of the map. Shoreside Vale was landlocked and I don't think they had an infinite ocean like there was in every other game, was there?
The police in III and VC both seemed to be overly-aggressive, but I don't think I minded that as much as I minded having to avoid most areas of Portland to avoid the gangs. That really is the biggest thing I dislike about the game, how they basically made it extremely hard to ever go back to St. Marks without a bulletproof vehicle. That and the overpowered shotguns that all of the Leone's were carrying that blow your car up in about two shots.