GTAIV was the first GTA game since it went 3D that I didn't experience falling through the world and visiting blue/brown/gray/whatever hell. It was quite polished... On the other hand, certain things annoyed the **** out of me the major things appear to have been addressed. Now hopefully they don't put in another version of the stupid packages with no point to do other than a stupid trophy.
I like having the hidden packages but they need to get you more then some stupid BS trophy or achievement, atleast unlocking the free weapons was a reward, most of the guns could be easily found but it was still better then getting jack **** which is what happened in GTA IV.
In GTA 3, VC, SA, LCS, and VCS the hidden packages unlocked free weapons at your safehouse, in GTA IV, TL&D, and TBoGT they unlocked 1 vehicle only which wasn't even worth it as you had to collect ALL the hidden packages just for one little reward. In GTA 3 era games every 10 packages or so you unlocked a free weapon at the safehouse.
"Always two there are, a master and an apprentice"
I loved having packages to collect, especially when there were different types like in SA. But in GTAIV, I didn't even try :/, however, the expansions gave more rewards for the seagulls I think, even if it still wasn't as good as he older games. Also, I feel that Liberty City isn't as fun to explore as San Andreas (or Los Santos for GTAV).
So I definitely have hope for GTAV, whatever I didn't like in GTAIV seems to have been made up for in the expansions (more or less, especially in TBoGT). Plus, Rockstar seems to take improvements from their other games (replaying missions from Gay Tony made it into Red Dead, the animals and random enconters from Red Dead going into GTA5 I think, etc).