You know, I gotta be honest (and since it's the subject of the thread :P), I wasn't too keen on Dream Theater first time around.  A friend of mine sent me Learning to Live and told me how great it was.  I listened to it and liked it, but it just wasn't what I was expecting, so it didn't resonate with me too well.
A few years later I give them a go, and listen to Forsaken.  I really dig it and go back to Images & Words and listen to Pull Me Under, Take the Time, Another Day and give Learning to Live another go.

Now I think Learning to Live is one of the greatest songs ever written and I cannot pick a single Dream Theater song I don't like in some way.