I heard the first half of it is better than the second, is it?
Yeah, definitely, but that's not saying that the second part is bad.
The thing is, some important stuff was left out, apparently cause Konami and Hideo Kojima broke up before finishing the game. And that becomes pretty obvious as you play the game, it's like, it instantly skips to the ending.
Also some fans are mad at this game, for a reason that involves huge spoilers so you better not google that.
Overall, it's a solid game (no pun intended)

. I've played them all, with the exception of Ground Zeroes, I think that if you liked previous MGS games you still will love this one.