There's no free content updates for the game. Destiny charges for packs of content, $20 for them I believe. Raids, strikes (dungeons), and quests are in them. The new expansion is $40 but I guess doesn't have much in it content-wise so people are upset. Also I guess there's some extra content if you buy the base game + expansion bundle for $60 and people who already own the base game are salty about having to buy it twice to get everything. Plus there's the issue with PS4 getting more content than X1 owners in each DLC but X1 owners still having to pay the same price.
I probably got some of that wrong but that's what I think are the issues.