As long as you’ve done the original Deimos open world stuff, you can just follow the main story to unlock gameplay systems.

Pablo has been cooking for the last couple of years. Most of the bad warframes received considerable buffs or reworks, and most of them will serve you well until the late-game missions (with the exception of Loki, Limbo, and Nekros; they’re pretty much useless now). Arcanes are even more busted than before. There are legitimate builds that don’t equip Energize. Melee Influence is the reigning king of melee arcanes. You can slap a basic electric status build on literally any melee weapon and have something that can take you to level cap.

Also, Stalker had a girlfriend and they’ve fucked.