I've noticed a trend; band's first release - often an EP - is very consistently different from the sound of their first album, many times for the worse.
When I find a new band I normally don't like to start with their first album, especially if the group has been around for awhile and released several full-lengths. I like to either begin with the most current album and work back, or start from album three, after the group has discovered their comfort level with their sound.
I do this because alot of times the sounds between albums vary drastically; either the band moves towards a more commercial sound, or the opposite, where the band dislikes the way it tried to posture itself for the masses and moves off the deep end. Very few groups keep the same sound all the way through their career.
And I'm not saying that a little bit of experimentation is bad, I like bands that let their sound grow with each release. Look at Clutch, they moved from a stoner metal/rock group to a funk rock sound and now they are cemented heavily within the blues. But the steps were small from album to album, not one album they are metal, and the next one they are blues.
The three groups I want to focus on - the examples where it is the most obvious - are Fishbone, Mammal, and Mechanical Poet.
Their next release, In Your Face, was just that, in your face. It was without all the humor of the EP (a little was stil there but not enough). The songs were darker and more punk then ska. It reminded me a little of Bad Brains, or some other classic punk rock band from the 70's - not as hardcore, but way more angry then their EP. The band continues this style for two more albums, then releases the downright metal album, Give a Monkey a Brain and He'll Swear He's the Center of the Universe, a complete 180 from their earlier days (but it is my favorite of their albums). And for the next few albums they meander back-and-forth between angry metal/punk, and lackadaisical psudo-punk (probably because they were signed to Disney's record label for a bit). It's all a bit eclectic, and nothing like their original sound.
Now that I have, I'm a little less excited about the band. Don't get me wrong, it's still good music, but it's not the original sound I fell in love with. Two of their following three releases are live albums (again trying to capture some of their excitement while live), and there are several good songs there, but as I've stated before, I'm not a fan of live albums.
Again the releases following their debut EP are pretty good, but it sounds like a different band altogether, and not for the better.
Psychotic Philosophy, and he wove a tale of a progressive folk symphonic band, utilizing Russian instruments (they are from Russia) and old Russian folk-lore stories. I was intrigued, so I quickly went out and 'acquired' all I could from the band. As I began to listen to this EP I was mesmerized, everything that I had read was true. The songs were great, and filled with instruments that I could not name, with a semi-story focusing in on man-created machines coming to life (sort of like that new movie that just came out, 9). I was captivated and I could not wait to hear their fist full-length, Woodland Prattlers.
Their next album, dialed back the folk, and the folk-instruments. It still had the soul of the Handmade Essence EP, but you could tell that the group was moving away from that sound, less folk and more symphonic-prog. With each subsequent release, the trand continued. By their third album, Who Did It To Michelle Waters?, their original sound was gone, filled with empty-sounding songs and a wishy-washy story. The next album, Eidoline: The Arrakeen Code, was more of the same, but there was a light at the end of the tunnel - another EP! Their latest release, Ghouls, was a revert back to the sound of their first full-length album. It is no Handmade Essence, but it is a step in the right direction. I hope they follow it up with a revert back to the days of old (at least for the band).
Well there you have it, three good bands that started as so much more. I know there are more, but these are the ones I can think of off the top of my head, and let's be honest - most transitions between demos or debut EPs are for the best. This is just a short list of the rare bands that shouldn't have changed their style.