So I just restarted this after stopping about a month ago, and I've got a few questions.
Are there any real differences in playing good or evil? I mean, different quests or anything?
Are there any quests I'll miss out on if I'm good rather than evil, and vice versa?
Is there any real way to track how much of the game I've completed, as far as stuff found and quests finished?
The good and evil part is hard to explain without ruining the game. There are a few parts in the story where you can make different choices that will have some affect on what you may experience. Like, if you decide to do something evil at one of these points you may get access to a different weapon, gain more money, and/or even have to fight a former ally to the death as a result. Or, if you pick the good side, you might lose out on money, retain allies and not get the weapon, but get respect of people, and maybe more experience. It varies.
A big issue with the game is that regardless of your choices, things seem amiss. As before, if you are forced to kill an ally, you lose them from the game. Yet, and this is what's weird, even if you don't kill them, they usually are never seen again. More bizarre is that their absence is rarely explained, and even if it is explained it makes little sense. So, in hindsight, you might as well just kill them if you're trying to get through the game quickly, as it rarely has any consequence. It's disappointing.
There is a somewhat midpoint part where you can make a seemingly small, but actually big decision, and that can affect the game slightly. Having not read guides, I didn't realize how important the part was until I was forced with an ultimatum. I then went online, after having made my choice and read about how there are alternate decisions, and how each of these affect the game.
I know I'm being vague, but that's on purpose. From what I've read, there doesn't seem to be any dramatic difference in most of the game, and your character behavior does little to influence the actual pivotal choices in the game. It's not like something like Mass Effect, where you need high levels of good or evil to get to make those choices. In this game, when you're faced with an in-game choice, you can usually tell which is good or bad. Those key choices can have influence on the narrative of the game, but usually the game experience remains the same regardless.
If you are really curious, you could always look online about what affects the game. It might ruin parts for you, but you can see which paths you might like to take. And don't forget that the game allows you multiple save slots, so you can try a decision, and if you don't like it revert to a previous save and see if you like the other choice(s) better.