I think a great mark of knowledge and prowess concerning this game is to beat it with the radar turned off. You can do this by pressing start and on the menu going to "display". There you can turn the radar from "on" to "off". Good luck! Many missions are a bit harder than usual you will find. It was a very fun challenge. The one have-to-do mission that was very hard verging on frustrating in this mode was 'Friendly Rivalry'. Twenty minutes in a helicopter later, though, I was home free. The other missions that would be very tough are optional.
I've also beaten this game starting each mission with no weapons or armor, but allowed to collect pick-ups during the missions. 'Death Row' is especially tough this way.
I've also beaten this game starting each mission with all the weapons I would need to beat each mission and not allowed to collect pick-ups during the mission.
I've also beaten this game without using L1 auto-aim once. You learn to use the Flamethrower, Kruger/M4, sniper, and Minigun a lot this way. Very fun challenge!
I've also beaten this game with the pedestrians riot and pedestrians have weapons cheat on the entire time. Another different and challenging way to play this game. Different strategies must be employed in certain missions/parts.
Next up, turning HUD display from "on" to "off". This way, I can't see $$$, health, armor, weapon ammo, or time. Should be a fun challenge!
Eleven and half years later I am still shamelessly obsessed with this game. Who else?
I beat the game with HUD mode turned off, and I have to say it may have been the most fun yet! Not that much more challenging than normal. I never did walk up to a green house icon and couldn't purchase it; I always had enough $$$ though I never knew how much. There were a few points during missions where I thought I should've died based on how much bullet damage I thought I was taking. There were a few instances in which I died easier than I thought based on how much damage I thought I had taken. I made sure to have full health and armor before triggering the harder missions. Always had enough ammo; probably overkill unbeknownst to me.
I used to play loads with HUD off when I was recording my stunt videos. I didn't find it too different, but then I wasn't attracting police attention or getting in shootouts (well, not very often anyway, and not usually deliberately).