I didn't like the realistic cover system. Mainly because I can't go on a killing spree like I could in Andreas. Get more then 5 cops on you and your screwed.
I love the hightened tension though, you know that it is easy to die. Being trapped in allyway with cops at both ends when you are almost out of ammo, take cover and cap one in the head, sprint out of the alleyway with 2 cops firing pistols at you, another cop out on the street, start running in the opposite direction, etc etc. I love that game. Might turn it on now.
For once I have to agree with fatass. I don't play GTA for the story or the challenge. I play GTA to murder people en masse.