Nah, Big Mama was awesome. Seeing Snake meeting and reconnecting with his surrogate mother, the reveals within the cutscene and then ending in a spectacular chase IF you played it with the cinematic camera. Also, you could hug her if you hold triangle which also works as a small cover. Even Big Boss was awesome, without him the game wouldn't have ended as memorably as it did "This is good, isn't it?"
It would have ended with either Snake killing himself which is the predictable route since all the trailers and also throughout the course of the game you just feel like YUP HE'S GONNA DIE IN THE END. The other ending would be him and Otacon getting executed which is pretty fucking stupid and not in a good way.
She thought it was BB's corpse(Well to fool the A.I patroits, for the greater good and all that shit).
Edit: I love MGS4, it's my favorite one but I know it has very loud haters as well. I'm in the boat that adores the first 5 games though. All of them are fantastic and each has their ups as well as downs.
But why would Solid Snake care if she was his surrogate, thats my issue Solid more than most of the other characters in the series is his own man. The emotion he shows toward Eva and Big Boss strikes as out of place and false when you look at who that character is.
If anything he should've been condemning them for their actions. Again it feels like absentee parents showing up when your thirty going "Sorry I never come around ever/ Sorry I tried to murder you twice can you helps us out of a bind?"