I got my Imperial Agent up to level 50 and finished the class storyline and also the main quest storyline. The Imperial Agent storyline (especially Light-side Imp Agent, in my opinion) was very, very good. Very spy-like, lots of twists and turns, betrayal, double/triple agents, etc. The main theme of the storyline, of how the non-Sith exist in an Empire ruled by the Sith, was really interesting.
I was expecting a lot of the traditional spy stuff, and that was there in spades. At one point, I was pretty sure I was a quintuple agent, which in retrospect makes no sense, but indicates the level of paranoia that was going on. But I was not expecting story elements to be based on Isaac Asimov's work. It was brilliant, and well thought out.
For tactics, I played Marksman Sniper. It worked fine for the most part, though it is rather weak until you get to about level 30 or so. At that point you get two abilities (one from talents, one trained) which are a core part of the rotation, and damage starts flowing.
The difficulty level is interesting too. In general, class quests were slightly easier than regular story quests, which does make class balance seem slightly questionable. Overall though, most fights were roughly the same difficulty, save two.
These two fights are significantly harder than all other fights, and it does seem rather odd. The first fight is the class fight at the end of Chapter 1. It doesn't help that it's pretty buggy. But the entire fight is based around interrupting, using any ability that can interrupt, including knockbacks.
The second hard fight is main quest boss at the end of Voss. When did pillar-humping become an acceptable PvE tactic? This fight is literally pillar-humping as you use two pillars to break line-of-sight while keeping dots up and the occasional instant.
Oh well, those two fights do seem a little out of character.
But now the question becomes what should I do? Should I start a new character and check out a new story? Should I try and do instances? Lots of choices here.