i say you could beat it pretty quick as long as you have the time to sit down, and rush them.
but thats kind of boring, and doesnt seem like thats how the game was meant to be enjoyed. its best to take your time and find secret things and explore, and gives you something to do when you are bored if you havent beaten it yet.
but if you want to beat it quickly thats your choice.
i only played the GTA3 and i think theres not that much missions as i remember, but takes awhile to achieve it, but i think you could do in like less than 6 hours maybe?
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