The Best Sequal
 

ac/dcs sequal from highway to hell to back in black
nirvana nevermind to in utero
joy division unkown pleasure to closer
david bowie hunky dory to ziggy stardust the rise and fall and the spiders from mars

Arch Enemy: From "Burning Bridges" to "Wages Of Sin" such vast change in style. Wonderful album!
Dark Tranquillity: From "Projector" to "Damage Done" I can't even listen to Projector it's so awful >_< but Damage Done is one of the best metal albums I have ever heard.
Dimmu Borgir: From "Spiritual Black Dimensions" to "Puritanical Euphoric Misanthropia" S.B.D. was a horrible follow up to "Enthrone Darkness Triumphant" but this band won me back with P.E.M.
Nightrage: From "Sweet Vengence" to "Decent Into Chaos" They got so much better over this span, I love their new CD
Devildriver: From "Devildriver" to "The Fury Of Our Maker's Hand" The new album is a improvment on this band who were rather bland when they started. I think by their next CD they will be pretty good.

Eh I could probly do this for awhile I'll stop now

By Sequal do you mean "Sophomore album"?

Since he listed multiple albums I just assumed he ment follow-ups. So anything can be a sequel but the first album or course

Rx Bandits - 'Progress' to 'The Resignation'
MxPx - 'Before Everything and After' to 'Panic' (as in 'vast improvement')
The Offspring - 'Ignition' to 'Smash'