I'm originally studied in natural science, so when I read philosophy I tend to put a lot of it into a scientific context, which usually supersedes whatever I'm reading and effectively stamps it out.
That said, I've heard that Heidegger's 'Being and Time' is incredibly influential, and so without actually reading the source work I'd like to know what valuable thought came out of this work?
This is going to be a somewhat difficult question to answer as people will have differing opinions on Heidegger. I'd say there's three main things people get from Heidegger, all of which are somewhat related.
(1) There's a famous passage about Zuhandenheit (being at hand) and Vorhandenheit (ready to hand) which expresses that we spend most of our time using things and less time thinking about things. The cash-out values are complex but one is that we only care about certain types of questions when things are going wrong.
(2) The other perhaps larger outcome that can be seen in this passage but also in quite a few other places is that Heidegger could be said to be the father of philosophical hermeneutics. The idea here is that we know things against a background. In Heidegger's case "world" or "the four fold" depending on the text that we stake out to give meaning to the things we do "driving this into earth." In simpler terms, he doesn't think there's a single bedrock reality that describes things "scientifically."
(3) Heidegger's main protagonist is "Da-Sein" which relates to both of these as the human being as he exists and finds himself in the world. Da-Sein is often distracted by "beings" that prevent him from thinking about the key questions (for Heidegger, this is the obtusely worded question of being). What Da-Sein is is ultimately a being that is already in time (Heidegger calls this Geworfenheit "thrownness"). Long story short, we're going to die and we need to stop distracting ourselves from this fact.
There may be some other things people get from Heidegger but I would say the top two are the biggest hits that non Heidegger scholars would know. The third one seems similar to Sartre and the existentialists but Heidegger rejects that label.
Another confusing feature in studying Heidegger is that he uses "metaphysics" and "ontology" in ways that differ from many of his predecessors. For many philosohpers, the terms are roughly synonymous. For Heidegger, "metaphysics" refers to the tradition of philosophical inquiry up until him and the confusion of beings with Being (i.e., a focus on the former rather the latter). Conversely, "ontology" is a term which he uses in complicated ways. When it refers to the project of understanding BEING through his modified phenomenological method, it is good. When it refers to the work others did before, it becomes "ontic" and is generally insufficient. Fundamental ontology is looking at THE QUESTION...
