I finished it and it's a fun game especially for marvel fans. Story mode will last around 8-10 hours and after that is free play. This was the first lego game I played to completion (I quit batman 2 after 4 hours) so it took me a little while to get acquainted with the gameplay. This made some puzzles take longer than necessary to solve. For example, in a level you must use black widow's cloaking mode to get past some security cameras and get to a door. That part was easy but I couldn't figure out what to do next. There were no buttons to press, nothing to break, no useful abilities from my heroes to proceed. After about five minutes I found out that black widow had to jump on a lever and pull it down. So for players with no previous experience with the lego games there's a bit of a learning curve and unfortunately no manual. That's a big negative since I had a hard time figuring out basic things like how to switch characters in free mode, why I was actually collecting legos, etc. I still don't know what the golden bricks or red bricks are for.
My reference for the Marvel universe are the comics I read as a kid, the Marvel Now! comics that I got back into and the various movies. The game's Marvel universe skews heavily toward the movies (particularly the Avengers) and doesn't have anything to do with the post Marvel Now! canon (Charles Xavier is alive, Peter Parker is still Spider-Man, Jean Grey isn't a teenager from the past etc.) The Avengers movie is the strongest influence with shield being at the center of the game.
The heroes you'll be using most are Hulk, Iron Man, Captain America, Spider-Man, Thor Wolverine and Mr. Fantastic. The rest of the fantastic four are also given a sizable role which isn't odd considering one of the main villains is Dr. Doom. The X-men's role is somewhat disappointing. You get to play as Wolverine a lot but there's only one level dedicated to the X-Men. In that level you play mostly as Cyclops and Jean Grey and eventually Iceman, Storm and for the boss battle Beast. Other than that level they only make a brief appearance.
Most of the large cast is fun to play as. You'll never get bored since there are so many different heroes to play as. Some they nailed (such as Hulk and Spider-Man) whereas a few they missed (Wolverine). With Wolverine the problem is that he has the same attack tempo as the other characters whereas you feel like he should be quickly slicing and dicing through the enemies. Another problem is how the flying characters attacks in flight. When you use your basic attack in flight you shoot in front of you but there's no way to aim. Since you're almost always overhead the enemies when you're flying you'll never hit them.
The voice acting is good for the most part although a couple of the voices are miscast (most notably Iron Man.) The only official actor is Clark Gregg as Agent Coulson but most of the other actors do a decent job of aping the moives voices of characters such as Loki and Nick Fury.
The game itself plays more like a big budget marvel game than a lego game. The only time you're really reminded that this is legos is when you're moving around New York and seeing the generic lego cars being driven around. Other than that, once you start playing it feels like you're in the Marvel universe rather than legoland.
Overall, I'd highly recommend the game to Marvel fans and would recommend casual Marvel fans to pick it up on sale.