Yep gone are the repetitive gameplay from the original Assasin's Creed.
I can't help to compare MGS4 with ACII. even the looting of the death is rather similar. The cities are quite huge too but luckily you can transport using,..ahem..'teleporting'. Well, u won't want to spend 10 to 15 mins riding your horse from one city to another.
The rpg elements with economics where you can spend money upgrading the towns, houses, buildings, upgrading your armor, health, etc are very well incorporated. It does gives you enormous amount of money and getting things opening up as you progresses. I must say the lip synching is getting better to somewhat reminiscense of disney animation with some body language and mannerism, it's really a joy to watch and play.