let me put it this way... I've finished Saint's Row 2. GTA has the production value, but Saint's Row is fun.
I'm in the same boat.
Another point worth making is that SR2 took the already fun formula of the first game and improved on it in every conceivable way.
On the other hand, after experiencing sandbox bliss in GTA:SA, GTAIV felt like a very significant step back in terms of the amount it allowed you to do. What you could do, it handled very well, but after San Andreas, IV was just a let down in almost every way. I hope Rockstar gives us another SA-like experience for the next one.