Trilian is fantastic. It'll take you a while to grasp just how immense and versatile it is, and the samples sound great. I find I have to HPF them a little more aggressively than most bass libraries though, don't know if anyone else has experienced that. I guess this means there is "more bass" to start off if you want it. One thing to remember is that if you're not using all of the articulations, you can load a "lite" version of the samples which uses considerably less memory. I find myself doing this most of the time.
But as others have said, check out the Groove3 tutorial by Eli Krantzberg. It's a fantastic course and will really unlock the power of Trilian for you. I was stumbling around in the dark until I watched it (although there are also lots of videos on the Spectrasonics site as well).