Too bad the list does not count live albums, since the first DT album I ever heard was Once in a LIVEtime, right when it came out. It was funny, cause at the time I was in my high school band studying all this music and a bunch of other guys in band were
huge fans of DT. I remember being really impressed by their musical complexity and dexterity. At the time, I wasn't really into prog bands like Rush or Yes (though my mom did have Asia's debut on vinyl, and I do recall liking that one quite a bit), I was more into bands like AC/DC, Ozzy, Alice Cooper, Sabbath, Scorpions, GnR and the like, but when I first heard Dream Theater it really struck a chord. I was a huge fan of Deep Purple at the time too, and the frequent use of classic hammond organ sounds by both Moore and Sherinian was another thing that drew me to the band. Oh, that and the fact that I immediately could tell that Petrucci was in the same league as Randy Rhodes or Yngwie. After hearing LIVEtime, I began checking out their back catalog starting with Awake, then Images and FII, as well as buying new albums like SfaM and SDoIT. Now I own all of their studio albums, most of their live ones and I've seen almost every show they've played in the Chicago area since the turn of the Millennium, and I haven't looked back since