Not bad, seems pretty fluffy. Also, welcome to Dakka
A few changes:
-Sniper Scouts + Land Speeder Storms don't really mix. Bolter Scouts in the
LSS go very well though (or shotgun Scouts.)
-You're going to need some more armor if you want to take transports. I'd suggest either predators or vindicators instead of your Centurions. Centurions also are very unfluffy for Raven Guard.
-Dreadnoughts with
CCW and Drop Pods pair very well. They also like to be paired. I highly recommend either changing it to a dakka dread or dropping him in. Both ways he should have a friend though.
-I'm a firm believe that plasma pistols are worthless. I would drop the plasma pistol for another flamer.
-Solo Land Speeders tend to get killed pretty quick, though suicide speeders with dual MMeltas are useful. If you armor up they can be pretty useful, otherwise I don't think they fit in as well with your list.