I've ignored Destruction and Illusion, with my focus being almost entirely Conjuration and Alteration. Restoration is my secondary tree which I am finding extremely difficult to level because I don't get hit enough; I need to take a companion out someday and just heal the shit out of them for a while I guess. I always play my mages super defensive like this in TES, but this time it has worked out for the best since Paralyze was moved to Alteration. Had Paralyze still been under Illusion I probably would not have wound up quite so lopsided towards my specialization schools, but it's worked out well. Not quite up to 100 Alteration yet so I don't know if Mass Paralysis is really worth it, but I can't imagine needing it anyway. I do, however, want Atronach just so I can be a complete mage-tank.