I suggest doing a perma-death playthrough on insanity.
IMHO this is usually the most fun self imposed challenge. It lets you still have all the normal options for variety in gameplay style, character builds, etc. While still making everything constantly tense and exciting, since slipping up for a couple seconds can always end Shep's life and that means game over. I've been trying to get through the game this way for a while and really enjoy it.
I do add three other stipulations to the challenge for myself. First, I can't use any of the DLC 'weapon pack' weapons. By this i mean the weapons that came as non-story dlc (venom, harrier, etc) and not the ones you get while playing the story DLCs like the lancer and raider. Second, I can't allow any incendiary ammo + power glitching (IA does stupid damage when combo'ed with warp, incinerate or incendiary grenades) so I have to either skip incendiary ammo or skip those powers (including on squadmates). Third, I have to do every mission/can't skip any combat related side quests.
The one thing I do to make it a little easier on myself is that I keep one save file that I make immediately after the intro stuff. Specifically I complete Mars, the Primarch rescue on Mennae and then the 10 or so non-combat side quests around the citadel + the search and rescue BS. After that I make one save that I keep and don't have to delete if I die. This saves you 4-5 hours of intro BS if you want to try another playthrough with the same class and honestly Mars and Mennae are so easy to survive that IDGAF about skipping them.
I'm far from an amazing player so the best I've managed is around 1/3 of the way through the total content (including the three story DLCs). Good luck and have fun if you try it!