I'm up to mission 25 in GTA IV, and so far, it's all been torture for me. I loved the trilogy, but never 100%'d them. Just did the main missions and beat the stories in them. So should I replay the trilogy and 100% them or move onto IV?
I personally like to finish a game I don't care for so I can give fully informed answers to why I didn't care for it. If you do 15 IV missions, reward yourself with working towards the Trilogy's 100% and simpy switch back and forth. It will gie you motivation to finish both.