[My general suggestions for the game]

These are my own suggestions and observations, any constructive criticism or other suggestions are welcome

It's tedious putting sigils on every Warframe for standing, you also have to sacrifice aesthetics if you're a fan of a different sigil, maybe have a separate system for this so we can have the best of both worlds. 
Warframe is a co-op game, yet the majority of the quests you cannot play in co-op. I think about how fun it was going through Halo 3 in co-op even if it didn't make much sense having 4 Chiefs, but I think Warframe is a game that should also have this.
Search bar for the navigation menu in the orbiter so you can find the mission/mode you want.
Add a simulacrum shortcut to the orbiter arsenal because 1 loading screen is better than 2.
The bronze>silver>gold every 3 mastery ranks doesn't look right, a mastery rank 22 player with a bronze portrait doesn't look very prestigious compared to the person that just got a gold mastery 21 symbol. Overwatch has a nice system for this.
Color correction should get a rework for consistency, it can look really nice and then it can look really bad (snow levels).
As a Vazarin player, it can be really hard to find my teammates in a fight to heal and make them immune, I think as part of the HUD rework we should get an option for teammates health bars to be more visible. Showing energy would also be nice for Zenurik/Trinity players.

Thanks for reading and sorry if the formatting is bad.