Couple of things:
the “I can kill a mob 5 levels above me but not touch a mob 6 levels above me” is straight from Vanilla WoW. As you noted, you just get a ton of resists and/or misses due to the level difference.
There’s no phasing as in WoW. You do have a lot of solo instances, especially for your storyline quests, where mobs won’t respawn and you won’t see other players, so that works in a lot of the same ways that phasing does (but on a personal level only).
The class quests are unique, but as mentioned above, all the quests (regular and Heroic) you get from the non-class guys are given to all characters.
The bonus quest series is a set of quests you get after you complete most of a planet’s storyline. It’s usually - but not always - given to you as you run to the spaceport to get the hell of that planet because you’re sick of it. The reward for the bonus series is always a quite nice item, and the quests are just regular quests, so it’s definitely worth doing it. Some of the bonus questlines happen later.
The quest (planet) progression is pretty linear. You’re stuck on your starter planet until you’re sent to your homeworld. You’re stuck on the homeworld until you get your ship. Then, as noted above, most classes get a “choice” of 2 quests - one of the appropriate level, and one 5 levels higher.
One thing I haven’t seen people talk about is how much the game opens up once you get off the homeworld (I recall discussions by some prior to the NDA dropping about how linear the planets were). My progression as a BH was Hutta -> Dromund Kass -> Balmorra -> Nar Shaddaa -> Tatooine -> Alderaan. I actually like the look of Dromund Kass, but it is a bit linear. Balmorra is better, Nar Shaddaa is worse (I really hate super-industrialized planets, Coruscant included). But Tatooine and Alderaan are really wide open, and when I fiddled with a level 40 a little while ago, Hoth was even more so.
@Instant: I played Assassin in a prior build and think they’re awesome. Not sure if your comments are more PVP oriented than PVE, because he could take on all sorts of mobs. I was putting points into the tanking tree so he had high survivability. But they’ve got all sorts of utility, which really appealed to me.
Your complaints about Operative healing are really due to not having a UI that’s suitable for healing. The UI really hamstrings healers, I think, and will lead to a bunch of healer frustration. I’m sure it will be improved, but it’s lacking now.
As to the min-maxing of Light/Dark points, it’s been noted for a while that there needs to be some sort of “neutral” gear. Someone asked why play a light side Empire character? So you can get good deals on all those pieces of gear on the Empire auction house that require Light I or Light II! Also, when you pick light side choices in the Empire, you can sort of RP a guy who thinks the system is too brutal and is working to soften it. Unfortunately, when you pick dark side choices as a Republic character, you’re just RPing a brutish jerk.