I got the game when it was on special offer for € 80, and some of the level packs for only € 24.
It's genuine Lego figures. They look nice on display, but are not a individual as the infinity figures.
There are no power discs or crystals.
There are fun packs: one figure and one item (vehicle, tool or so),
team packs: Two figures and two items
level packs: a figure and two items, and the figure unlocks access to a new playable level.
Example: Ghostbusters level pack with Venkman unlocks the Ghostbusters level (story based on the first movie) and free play world. Something like an island, themed by Ghostbusters2 New York
If you get only the Slimer or Stay Puft fun pack they unlock only the free play world.
Startpack gives you Gandalf, Wildstyle and Batman with his car, a story with 15 chapters (about 8 hours + playtime, depending how many 'sidequests you do in addition), and the Lord of Rings, lego Movie and DC World free play worlds. You can get all achievements/platinum trophy with the starter kit.
Catch and big difference to Infinity is that every character has a skill set to use in the game (Mind control, flying, diving, cutting gold, cutting silver, catching ghosts etc). Many figures you can rent in-game for studds for 30 seconds by now, and solve little tasks like opening doors, hacking terminals, blowing through walls etc. However if you want to dive you need to buy a character or vehicle with that ability.
Second big difference: No creativity. You cannot build anything by yourself, no levels no places.
I really like it. Played through the story twice so far. A second time after a few months and getting some more figures. Gameplay is pretty much like in other lego games. If you never played a lego game, you should try downloading a demo of Jurassic World or Marvel and see if you like that smashing and building thing
There are no rare collectibles. I think Dr. Who was amazon exclusive, but basically you can get ever pack anywhere.