Tyranids are the worst of the 5th codexes. With that said, they're still a solid codex. On a scale of 1-10, they're a 7. There are a few builds where you've got some serious work cut out for you, but in a TAC setting, Tyranids aren't too bad off. I've only ever run into one list where I felt I had no chance to win (Venomspam go!) and a handful where I knew I needed some serious luck (SM Bikes, Parking lot).
I don't feel Tyranids were nerfed in the 4-5th codex update, it was more of a lateral change. We gained and we lost. Honestly I think the FAQ did more damage than the codex change.