As far as I noticed, Sieges Even haven´t been mentioned yet. While their first album "Life Cycle" sounds a bit similar to Watchtower´s "Control And Resistance" (though it was released a year earlier), their other albums don´t remind me of any other bands I know and they also all sound different from each other. If you don´t like Watchtower, you should still try "Steps", "A Sense Of Change" and "Sophisticated". I only wish one of the vocalists on the latter two had already sung on "Steps" and "Life Cylce", because I think the vocalist on these two albums was definitely the weakest part in the band. (Though I still like both albums.)
Though they might not be considered "progressive" in the sense this term is usually used, you should also try Atrox and their albums "Contentum", "Terrestrials" and "Orgasm". They are (or should I say were?) definitely unique (especially because of their - former - vocalist) and there´s also heaviness (probably mostly on "Orgasm") and complexity (probably mostly on "Terrestrials"). Check out the mp3-files from their aforementioned albums in the "More mp3´s"-section on their official website to find out whether they are what you´re looking for or not.
Though they might not be considered "progressive" in the sense this term is usually used, you should also try Atrox and their albums "Contentum", "Terrestrials" and "Orgasm". They are (or should I say were?) definitely unique (especially because of their - former - vocalist) and there´s also heaviness (probably mostly on "Orgasm") and complexity (probably mostly on "Terrestrials"). Check out the mp3-files from their aforementioned albums in the "More mp3´s"-section on their official website to find out whether they are what you´re looking for or not.