The following spells need to be re-assessed. They are the spells that fail in both PvE and PvP situations.
Shadowflame - Damage is not worth the cooldown, cone range is extremely limited. Without the glyph, this spell would be completely useless in PvP as well as PvE. I know Blizzard don't want to use glyphs in order to make a spell useful, so my suggestion would be to give it some utility (and/or increase damage). Give it a stock 50-70% snare while increasing the cone range to 10 yards. Change the glyph to reduce cooldown or remove snare but increase damage (for PvE).
Inferno - No brainer, this pet is a net DPS loss no matter what spec you have. No reason to ever summon this guy other than as a gimmick. Suggestion would be to keep it as is but make it summonable while you have a pet out.
Ritual of Doom - Same as above. This guy is a little too strong to be a complimentary to your existing pet, so I suggest you just flat out increase the damage on this guy. Give him his own niche, like as an AoE pet (buff his rain of fire?)
Hellfire - Hands down our most useless spell thus far. There is absolutely NO reason to ever use this spell other than wanting to kill yourself without a durability loss. Less damage than RoF, requires melee range, does damage to you, this spell is so bad now, it's laughable.
Curses - Debuff curses like CoE and CoW need to be reworked. I suggest combining them into the DPS curses. Such as, make CoD also increase spell damage on target by 13% and make CoA decrease target AP/armor. Problem solved.
Drain Mana - Is this spell ever used any more since the PvP nerf? It was never that useful in PvE, now it's also pretty useless in PvP as well. It''s channeled with limited range. Suggestion? I dunno... Nothing really can be done other than increasing its power 10 fold on PvE to make it useful on bosses like Deathwhisper...