Very Cool, I love Devastators, I wish I had that many.
If I were you I'd make the tac squad have fewer guys and go with a ten many scout sniper team. You can attempt to pin the enemy that poses a danger with a melta or something. I don't think the flamer or 1 ML will be missed.
Also, I'd keep the Devastator Squads with the same weapon, like you did the first four. Maybe all plasma and all ML for the last two. Is there areason you mixed them up?
Also, please give us some battle reports on this list, just curious how it goes for you. Good Luck!