Some of the Lego titles have been a bit too advanced for my 4 yr old to keep up with my 7 yr old, including the first Lego Batman. However, they have a lot more freedom in Lego Batman 2.
The open city (instead of being restricted to freeplay, the headquarters or mission areas) makes it much easier for my kids to jump in and play together.
They don't have to stay together once in the city and if one needs help, the other can drop out and come back in next to the player that needs help. Or, they have the option to let 1 player and the CPU character complete a difficult part of a mission and join up when things are easier.
The best part for both ages is the super heros available in this version. With a little help, they were able to learn how to unlock and buy heroes like Superman, Green Lantern, Flash and more...
As a longtime LEGO game fan I count down the days to their next release. And sometimes I am greatly disappointed (Indiana Jones 2), and sometimes my hopes are wildly fulfilled (Harry Potter). I'm split on Batman 2 - parts are great, and parts are dull, monotonous.
To be more specific, the levels are great and really fun (though with the occasional glitch that has become the charming series hallmark). There are only about 12-15 of them though - down to about 1/2 the number that the original had.
To make up for that they have made Gotham City the overworld hub, similar to Hogwarts in the HP installments. Gotham is huge, filled with identical buildings, identical skyscrapers, identical streets, and a bewildering "map" in the upper-left corner whose sole purpose is dance random pictures down a line at you. Instead of being able to orient yourself NESW, you can guess the direction of various things (blue swirl, red line, etc) and then start moving in the direction of those things until they disappear and you have no idea what you were following anyway. To find your way around, you can use the actual map (a different map screen) which works well enough but you'll need to pull it up constantly to really be able to monitor your progress. Or you can FLYYYYY! Or try to anyway. Flying works great in the levels, but when attempted in Gotham it turns into a barely controllable mess.
There are some areas (like the Amusement Park) that are actually fun to explore and have creatively hidden blocks & things to find/do. Unfortunately, the vast majority of the hidden items in the Overworld basically consist of constantly referencing the map to wander over to where it seems like it will be, move aimlessly a little until you see some bouncing objects to hit, or a man being eaten by a piranha plant to be saved. Now do it ONE HUNDRED MORE TIMES.
Anyways, not the WORST but not the best LEGO game by a long shot. I recommend playing it, until you get bored.