Several readers asked about if plable party members are always the same. Based 20 hours of gameplay, you can only control Saren, Noel and one of the monster. Each monster can only be one role, ie. Commando, Ravenger, etc.
If another character temporary joins the team, ie. in one of the time segment, Snow was hanging around and during battles, he will fight with Sareh, Noel and monster but you have no control over him. At the first 20 minutes in the game opening, you control Lightning and then Noel briefly.
As for towns, each time segment you visit either has small town that you can run through in a few seconds or big city that puts you in a linear path like XIII. There is no shop to do shipping. You find a girl dressed like a bird standing around at different parts of the map. I wish they use XIII shopping cube because the she has horrible voice actor and say strangest things.
As for not failing the battle when the leader knocked out, both Sareh and Noel cannot be knocked out with the monster only alive in the battle.
As for upgrading the characters roles, I don't like not able to move the tree and see how many steps it takes to reach new abilities down the tree. It tells you what next level to unlock the next ability. In XIII, I plan way in advance what abilities I plan to unlock as each character gains more CP. XIII-2 is most upgrading blindly and only know the next ability. The monster abilities can only be upgraded by feeding them items you found after defeating enemies. That's good because I have use of them than just collecting them to sell. But the monsters don't have as many abilities like the humans. This makes harder to have two synegists enhancing your team quicker or two saboteurs weaking the enemies faster since the monster in your party only have a few skills.
Between Chapter 1 to 3b, you travel to places in XIII in the 1st 16 hours. They are kind of boring since you just battle random enemies and find the key to unlock other time portals. Once time segment for Chapter 4 is unlocked, you can also visit the Casino before proceeding. Sareh and Noel even said they are taking a break in the Casino. I didn't have time to play the games there. Once you get to Chapter 4, that's when you are in the new places and it plays very linear going in one path like XIII. You have to turn cube directions to open up paths to proceed up the elevators going up the tower. And tons of tougher enemies that will keep attacking after you make a few steps as you get close to the top of the tower at 20 hours into the game. I only have time to reach the top of the tower before having to return my rental. I think after the top tower, they finally get to meet Lightning.
Hopefully this partial game walkthrough with minimal spoiler gives you some idea how the game plays.
Complete Japanese edition video walkthrough:http://www.youtube.com/playlist?list=PLF99C1DA81235E8B6