That's the main thing about GTA IV that i don't like. The tasks aren't complex enough. It's always 'drive to deal, deal goes wrong, kill some people, escape police'. In San Andreas, the tasks were different, if not more complex or realistic.
I agree, the heist itself was a little unrealistic (especially when you're supposed to parachute to the helicopter, but it's physically impossible, and you end up with no police chasing you). However, I was thinking more of the planning that was involved, that lead up to the heist. If there had been some more planning for the bank robbery, it would've been more fun. I have to admit, I did love that mission though.
Indeed, I missed the planning part of the heist but IMO it was the best mission in the game.
I also loved how GTA is getting more emotional, hope the next one will have more moral choices and shit.