I've been looking at the comments in the Update 9 page and I figured out there were 2 major complaints (which were pretty obvious so I'm just being Captain Obvious):
1) The game has become too hard, DE sucks
2) The game has no difference from before, this update only added more bugs
3) There are also complaints about the Aura system (credits to the random Wikia contributer)
This is just my own opinion so feel free to do whatever you want to do about it:
for the people in 1), the developers are human, they have limits, don't complain about how the game is not up to your own taste. Yes, the game got harder but that was because people had been playing solo instead of online (not to mention the complaints about the game becoming too easy). This game is a CO-OP game so it was meant to play with other people. There are also others who complain about how the match lobby hasn't been developed. I'll just reply with the standard reply: this game is in beta, there will obviously be some parts of the game which isn't full developed, stop thinking that it's a fully released game, yes it looks nearly perfect but that's only because the developers had been working on the 'larger' parts (e.g Warframes, weapons) but hadn't managed to work on the 'smaller' things.
For 2), If there wasn't much of a difference, don't try to flaunt how great you are everywhere, there are people who wouldn't have been able to get hold of good weapons and Warframes since they could have started recently. You might be flaunting to people who have the starter items and can't get past the lower levels because of the Nightmare mode blocking their progression. However, if you still feel like flaunting your 'skills' to these people, please remember, you sound like an adult flaunting how you are more of a genius than an infant. However, I'll agree with the bugs, there are a lot of bugs in there but the developers are only human, they aren't perfect.
the complainers in 3) well, I have to agree on the fact that the Auras were a bad idea for both new an old players, for the new players, the energy space is a waste while for the old players, maxing it out and having 4 people using the same max Aura breaks the game, but this made people want to actually farm Auras (in theory anyway) so it has its pros and cons.
(I forsee some rage comments, but this just my own opinion so don't hold back, I'll like to see what you guys have to say)