The new Rotom forms are going to be even better than I expected. Retaining the ghost/electric typing is fine, but keeping Levitate is a godsend.
Spin Rotom can absolutely destroy Heracross, and for that matter, the majority of fighting types who are weak to Air Slash.
Heat Rotom as I said earlier in this thread will be great for SD Lucario, Heracross, Steelix, shit, this thing will even be able to take out Mamoswine.
Cut Rotom will be useful for all of those bulky grounds, and it will be able to beat up every bulky water without question. This can also counter Mamoswine.
Wash Rotom will perform like Cut, but it won't beat Swampert as easily. This could be useful for Mamoswine again, as well as Steelix. This gives Gliscor problems too.
Frost Form, ehh, would be useful on Hail teams. 100% Blizzard paired with STAB Thunderbolt and Shadow Ball from 105 base special attack is likely going to be scary.
I think these new forms will improve to BL atleast, due to having such nice resistances and improved defensive stats compared to normal form. They also gain powerful moves, meaning if you have a weakness to a specific threat, such as Mamoswine, you don't need to throw a Cresselia on your team anymore.