Welcome, Scar. I truly love all of their albums, so you really cannot go wrong. Based on what you said you like, I might recommend the following:
1. Scenes From A Memory: A concept album based upon some of the musical themes in the song Metropolis, pt. 1 from Images & Words.
2. A Dramatic Turn of Events: Their first album with Mike Mangini on drums. The band sounds more "modern" and "up to date," and their songwriting has matured and become more refined, but this album still manages to evoke a lot of similar sounds as Images & Words.
3. The Astonishing: Do not do this one next after only Images & Words. It is different, even for Dream Theater. It is a VERY long rock opera that is very complex, but may be a bit offputting to a newer fan. Still, in many respects, the sound is not drastically different than some of the other bands you mentioned.
4. Dream Theater (self titled): Overall, this album has shorter, more traditional song structures than a lot of Dream Theater's other albums (except for the long epic at the end of the album), while still somehow retaining that signature DT complexity.
Hope that helps.