It's a great game that deserves a lot of the praise it's getting, but it's far from flawless. The story, characters and atmosphere are what the game focuses on.
There are a few categories of collectibles to get throughout the game; the audio diaries are back, but they added telescopes and kinetoscopes into the game to help further the exploration and story. You can also find infusions and gear hidden throughout the game that help to boost your player.
If it's a game you want to get lost in, there's plenty to explore and take in. If you want it to be linear, then it's easy to let the game do that.
I'd agree and I'd say it is a bit more linear then Bioshock even with the telescopes and kinetoscopes (though I did not find all of them or the audio diaries so need to look even harder on the 2nd playthrough). I recall there just being huge areas in Rapture that you never had to set foot in once if you didn't want to, while I didn't get that sense in Columbia (something I assume the DLC will add on to). I think the plot in infinite is so much more immersive, especially as the game goes on that you find yourself torn away from exploration because you want to find out what happens next so badly.
Definitely wasn't flawless since it was brought it. Actually if you strip it down to just gameplay I'd say it is a rather average shooter, something I'd say about the 1st one too. It is the enviorment, story, characters and setting that makes it so excellent. A forbes review put it best, it is very rare for a game to have plot and writing at such a high level with gameplay that matches it, and vice versa. They used the Portal games as the rare example of such a god tier game (one I agree with) no knock at Infinite though as it still very excellent. I think some breaks in all the action could of helped, maybe some powers based puzzles or more side quests.
Why I still hold Half Life 2 in such high regard. Valve seems to know best how to balence things for a player. They throw just enough combat at you to get you pumped, but know when to turn it down so it doesn't become a meat grinder and know when to use a puzzle or plot time to give the player a breather.
I see that Levine likes to view combat as the puzzles in game, and things are definitely a lot more balenced then bioshock (bascially shock and shoot was all you ever needed) most battles didn't need as much creativity as maybe he intended. IDK nitpicking stuff here obviously.
End rant, everyone should at least try this game and try to get immersed in Columbia. Well worth the ride.