The internet, especially for us gamers, is a very vocal place filled with keyboard warriors and think-they-know-it-alls. It is also extremely negative. So many times i have seen people moan that "unit/codex X is worthless" when they've seen what one person on the internet said about one experience. The Internet is wrong.
Lets take Chaos Space Marines for example. I have seen many times people say the only good things in the book are cultists (because they're dirt cheap) and helldrakes (because they're helldrakes). They've also said Daemon Prince is worthless now he's not an eternal warrior.
I play pure Nurgle to the extent that if it can't take MoN it doesn't go in. That means i have not used a helldrake. Ever. Chaos Space Marines are currently my second best army (out of 4) loosing only to Necrons and even then not by a lot. I also field Gary (my Daemon Prince) and a unit of Spawn. According to the Internet that is they are some of the worst possible units to take in the book, yet they are some of my top units. It all comes down to how you use them and whether you can get past the negatives. Gary flies up the board with a 3+ cover save turn 1 then smacks the ever living snot out of what ever squad he finds. Spawn are incredibly fast and couldn't care less about that terrain in their way, they can also (potentially) put out an ungodly number of attacks and nurgle makes them T6. OK no save but you've got to wound them first and they're only 180 points for 5 beasts with T6 and 3 wounds each. Plague Marines. 1 point more than in the old codex. Internet's response "OH NO THEY'VE GONE UP THEY'RE WAAAAAAAYYY OVER COSTED NOW". my response "poisoned CCW's for 1 point, FANTASTIC".
I would move on to Dark Angels next but The Watcher (yes i've found you, and The Artisan too) has already done one on them - Link