1. It is a all-in-one news source. There are a lot of features that allow you to monitor the news from many different sources in real time.
2. It is a social network. The built-in chat and email service is _really_ basic. But, just about every one working in Finance is on it, with their contact details and resumes. As a trader, you can legally close financial transactions on the Bloomberg chat, as one would over the phone.
3. It is a data sharing platform. Banks and other market participants contribute to Bloomberg data by sending information that is normally not visible in the market. For instance FX volatilities are quoted by banks on bloomberg in real time. This information is only available in few places.
4. It is an API that allows its users to use its data for custom analytics.
5. It is an execution platform, where you can book trades, follow their values and risk when the market moves, etc.
6. It is open to 3rd parties: some banks and other data vendors have their own pages on bloomberg (which I never had access to).
7. It has many many other stuffs. There is a restaurant review system. There is a classified section. There are things to monitor the weather. It has videos, maps, it's just huge.
Now - that is what people are interested in.
And then there are the things that Bloomberg shoves down your throat. Like the keyboard.
Bloomberg _forces_ you to buy their keyboards, at a very heavy price. The justification is the fingerprint reader, but that's really just a scam, because they put a $10 fingerprint reader onto a $10 keyboard, and sell you the thing at $500 a piece. So you either need to buy the keyboard, or you need to buy the B-Unit, which is Bloomberg very 2-factor authentication device which I assume is also quite expensive.
There is also the additional price you pay for API access, or to be able to see very specialized data. You pay for your private circuit to their servers (yep, it usually doesn't go through the internet).
Also a few words on the UI: it is f-ing terrible. Hit Escape, and you will find yourself on the start page. It doesn't matter that you were in the middle of typing an email or pricing a product, it just restarts your terminal. Most of the features are accessed by obscure four letter codes, that one has to learn to go back to. There is a search feature but everything is mixed in, and so you have to be pretty lucky to find anything useful using that. After a while though, the fact that the UI is so bad makes you feel "part of the club", I think many people would hate it if it changed.