Weather change, adding storms or something to change the environment on each planet at random times. Snow, rain, floods, sandstorm, meteor showers. These things can take at certain times in certain places to where they would do damage to a guardian or make it a obstacle to get to certain places. Time change, not real time but some type of time change that will go from day to night. At night it would lead to certain objects not be fully visible to where you could set up an ambush on a random timer. Or make it a challenge to find certain things etc More game modes, like sparrow racing or something that h as to deal with our ships. Crucible can entertain guardians. But the lack of modes won't break you from the monotony.