I liked the whole "Nightsisters" trilogy pretty well. I didn't think it was as "oh my goodness" amazing as we seemed to hear in many reviews coming out of those theatrical screenings, but it was a definite improvement over poisoned juices and senate mumbo jumbo. Personally, I thought the battle between Dooku/Ventress/Oppress was kind of neat. The Oppress character is pretty cool too, but the main problem I have with him is his power levels are a bit crazy.
I've sort of felt the same, at times, about Cad Bane - as cool as I think he is. It seems like they really want to make sure you know these new baddies are "bad ass" or something. I can understand either of them being good fighters, and maybe even taking out some red-shirt Jedis or something, but as far as I'm concerned - particularly in the case of Bane - if they run across a Jedi the level of Windu, Kenobi, or Skywalker, they should be toast. Same thing with Oppress. Not only does he somewhat easily handle Kenobi and Skywalker at the same time, he also seemed to do pretty well against Dooku and Ventress, despite just "learning" the dark side very recently. I suppose it has something to do the powering up the Nightsisters gave him and everything, but it seemed a little extreme.
Also, am I reading the ending wrong, or is that saying that Darth Maul is somehow alive? It is funny to me how Lucas seems to be out of touch in a way with what the audience thinks will be cool. He killed Fett off quickly in the OT, and then was surprised that he was so popular and has been trying to recapture that with AOTC, the Mandos/Pre Vizla in CW, etc. Then, Maul is basically the best thing to come out of TPM and everyone seems to agree he's pretty cool, and he gets killed off quickly as well. Now we have Oppress, more of the Zabrak species, and possibly the return of Darth Maul as well.
Overall, the arc was pretty cool, and again - if they are watching - I think kids would enjoy Oppress for what he is as well. It was really cool seeing the Republic Commandos, and I hope we see more of them as well. As far as treading on EU stuff, I guess I'm just not familiar enough with the majority of it to notice. I know there are a lot of arguments for canon and all of that, but to me, the movies take first precedence, with the CW series second. They are both involving the creator, Lucas, first hand and are also experienced by the largest audiences. That's not saying there aren't great books, comics, etc - but seriously, it would get pretty difficult to reconcile all of that stuff without stepping on anything. If it was written by someone other than Lucas or someone involved with the movies/animated series, I don't have as much of a problem with changes. When they overwrite movies and what happened there, that is a bit different.