Voted for broforce!!
Ok, is battleblock worth playing solo?
Very much so, I enjoyed it all the way through purely as a single player as a platformer it hits all the right notes even if outside of it's amusing presentation (that story intro), does nothing too different or unique. Still, I went for every gem, I got the hidden areas, and downloaded harder custom made stages over the course of a year (console version) or so and I look fondly back on it.
I however do not recommend it if you are looking for a game to greatly challenge your skill in the vein of Super Meat Boy nor getting pitch perfect rhythm like Rayman Origins/Legends. It's a type like Gish or Adventues of Shuggy or Joe Danger where figuring out what to do and doing it at your own pace is the best course of action, and then trying for a good time afterward.
What DLC is a must for Sleeping Dogs?
I don't believe any are must haves, but Nightmare In North Point and Year of the Snake are good if you want more story near the end of the game, Zodiac Tournament if you want more fighting.
is Tomb Raider GOTY worth it? it's just multiplayer stuff right?
Not worth it, get the original version if it's cheaper. The Tomb of the Lost Adventurer is the only somewhat okay one, but it's small and doesn't add much and you can get that on it's own rather than spending more money for multiplayer aspects that isn't even alive online any more.