My (7 year old) son bought this set first, and has subsequently collected several other Ninjago characters. This is the only set in which you get the arena in which to spin (essential to define the playing area and stop spinners flying across the room).
The set includes one goodie Ninja (Jay) and one baddie Skeleton (Frakjaw), their spinners, 3 weapons apiece, the arena (just rods and connectors to make an oval shape) and a selection of 8 game cards; everything you need to start you off.
It is very easy to assemble everything, and play is simple.
As with all the Lego games you can vary the basic rules to make it all more interesting. Try playing with teams of 2 or 3 characters when you have collected more - we find it makes for longer more interesting games. We have also experimented with picking game cards at random from a shuffled face-down pile instead of just choosing your favourites at the start of a game; this works especially well when you have enough characters to create a team.