Just recently the reward for completing a mission just doesn't justify the effort needed to finish it. Never mind the frustration of never really feeling like some space ninja. It's impossible to actually do a stealth mission, even if you are super careful to kill all the enemy without raising an alarm it just goes and re-spawns them behind you anyway making it a waste of time. I'm now encountering enemy that are killing my level 30 warframes with one shot - no matter what mods I have on board or what HP\Shields I have. I guess this is the point where they have you start spending money on buffing up if you want to progress any further. But I don't see the point in that, it's not like you get a better experience for your money. Just the same only slightly less frustrating!