In Sides and the Brown Album are both absolutely essential, then Snivilisation. Don't bother with The Altogether. Both are definitely in the realm of techno, but, like Underworld, theres so much more going on than just pounding beats.
Overall, their sound is as broad as Underworld - their albums are all slightly different, there are lots of gems on hard to find EPs, and they have done soundtrack work as well, but speaking as someone that has everything they've released, the above should get you interested
