This expansion picks up right where the base game left off, in fact the campaign is mainly a retread of that original campaign. Admittedly there is a fun twist in the story, but that doesn't translate into much game play changes.
That's not what we're here for though, this expansion is about new heroes. Four new heroes with new abilities and powers to play with. And play with them you will, you'll almost have to if you want to make the best use of them.
The heroes in the base game were fairly balanced, you could grab pretty much any combination and do well in any scenario. The Night Squad team are very focused on a particular role. Night Vigilante for example is dedicated to value tests, the majority of his powers give bonuses to himself or teammates in succeeding at these. He does have a few good combat abilities, but his cards a leaning heavily on mental checks. If you just randomly pick heroes you could end up sorely lacking in some skill.
Depending on how you play this might be good or bad. It adds a new layer of strategy, which I like. However, it does mean you can't simply grab your favorite characters to form a team. Since there's nothing saying that you can't grab your favorite action figure to use instead of the character from the game I'm in favor of anything that puts more decisions in front of the players.
There are a few new game tiles in the box as well. The way the tiles are designed in this game makes more of them always a good thing. Since the tiles come labeled as a particular type and have cards explaining effects and objectives in them, you can randomly choose one tile of each type (maybe a few extra trap tiles) and generate a playable scenario. These new tiles fit seamlessly into what was in the base game. Adding more variety can only lead to more replays before things get stale.
I do want to mention that the trap tiles are more fun than the traps in the base game. The original traps really just had different damage effects, which is fine but the heroes are fast enough that often they weren't major factors. These new ones imprison heroes and teleport enemies around the map, they don't need to be used often to have an effect.
I guess it's good that the tiles are fun, since that's all the villain gets. I guess the Terror Trio expansion has more villain options, so maybe this balances things out.
If you're playing as the heroes or with some sort of automated villains, then this expansion will be perfect for you. If you're playing as the villains, then this does almost nothing to keep the game fresh.