SIGN... rubbish? Blasphemy! It got me into anime, and that makes it great. Without it, I wouldn't be sharing my insight with you.
Compared to roots, SIGN is fast-paced. The key difference between the two is that SIGN has a story of its own; complete with its own characters. roots, on the other hand, has the same lead as the G.U. games and can only go up to the very start of the G.U. story.
Also, if you've ever heard any of Ali Projects 'music' before, you'll have a good idea how WONDERFUL the soundtrack of roots is. The only good music is the OP.