Since I love this game, I guess I'll come to its defense.
1. I will concede right away that sometimes I got pissed at falling off of ledges because Starkiller feels the need to keep stepping forward as he attacks. That's a pain, but it wasn't exactly ruining the experience for me because I just decided it was a bad idea to attack towards a ledge I'm close to. As for the environment navigation being compared to Assassin's creed, this is just not that kind of game. I'd certainly enjoy being able to explore a little more in the sequel, but I definitely didn't feel like it was missing.
2. I don't know what to tell you about immersion. The cutscenes of the game make the plot pretty clear and the environments are gorgeous. It might seem like not much is going on yet because you just beat the second level. Try playing the whole game. Linear stupidness is pretty much any game with levels. As for humans not looking human, I think they do and don't really know what you're getting at there.
3. Physics 101- don't jump on slanty things. I got killed the same way, with the platform being too low, and it made me pretty mad all of one time. It's a stupid glitch, but perfectly avoidable.
4. If you had watched the cutscenes, you would know at this point that Vader is training Starkiller in killing Jedi so that they can defeat the Emperor together.
5. The holocrons are supposed to be hard to get. They're bonuses.
"Everything I tell you is a lie. Every question I ask you is a trick. You will find no truth in me."
―Vergere to Jacen Solo