LEGO Batman 2: DC Super Heroes introduced two features to LEGO Traveler's Tales games:
voice acting (instead of phantomimes) and Checkpoints (so now you don't have to worry about starting over from the beginning if you leave mid-way.)

You don't have to buy the first LEGO Batman game in order to understand the story of the sequel. Both stories are stand-alone.
Infact, LEGO Batman 2 feels more like a reboot than a sequel, because Gotham City in this game doesn't really resemble the Gotham City in the first game.
Not only that, but the Bat Cave is also radically different.

Unlike the first few LEGO TT games, campaign levels are unlocked in an open world, rather than in a small indoor environment.

Campaign gameplay mostly revolves around playing as Batman (of course), Robin and Superman.
The other members of the Justice League don't show up until later in the campaign.

Aside from playing through the main campaign and replaying it in free play mode, there are oodles of things to find and unlock in the open world.

Unfortunately, this game (the PC version) is not without glitches.
Sometimes, the keys will freeze and I would have to pull up the task manager to unfreeze them.
Another glitch is a spontaneous non-stop cycle through the collection of characters in Free Play mode.
One time, there was a serious glitch in which the screen froze at a cutscene, so I had to shut the computer down and redo the level.
Fortunately, I never encountered that last glitch again.

Final notes:
*If you like collecting things and boss battles, I recommend this as a LEGO video game.
*If you are a hardcore Batman fan and love Batman: The Animated Series, I think you'll enjoy the first LEGO Batman game more.
The first LEGO Batman resembled BTAS more, and had more of that Batman feel to it.
*If you aren't a hardcore Batman fan, but Batman is your favorite superhero and you are passionate about the rest of the DC Universe,
I think you'll enjoy playing this with your family.