I watched the series, and enjoyed it, just like many others did.
And if you love the series and cannot get enough of it then these graphic novels will be right up your street. However, the one thing that really annoyed me about these graphic novels is the fact that there is no real continuation of a story, every issue inside each g.novel is different, and seemingly pointless.
Tenchi was entertaining the first time I read it, but afterwards (and after 4 g.novels) I got a bit bored with the same "Tenchi finds problem, solves it, and Ryoko and Ayeka fight over Tenchi" sequence. Like I said, if you can't get enough of the series, buy this, but be warned, the g.novels do not give you any more of the kind of story found in the series (and you could watch the series for free, or relatively free (Its always on Cartoon Network), but it's 12 quid a pop for the "winning formula" of the g.novels).
If you want this story for any sort of swordplay (because Tenchi generally has this sort of a confrontation), then I can introduce you to two new swordsmen, infinately better than Tenchi:
1: Manji from "Blade of the Immortal" (My favourate g.novel series-I strongly recommend it)
2:Itto Ogami of "Lone Wolf and Cub" (Another great samurai g.novel series)