For the pessimistic, its just another piece of software. But there are many things that get together to make a great ecosystem. An ecosystem not only with community developers but also a strong support of the industry.
The first credit goes to the Eclipse Foundation. It is a not-for-profit organization. It is the umbrella body. It is the driving body behind the complete Ecosystem. The body that takes utmost care to keep Eclipse vendor-neutral.
You can read more about The Eclipse Foundation in detail at http://www.eclipse.org/org/
I am not legal expert. Please talk to your legal adviser for further clarifications.
EPL is not Yet Another Open Source License. On the middle ground, it is both industry-friendly and an OSI Approved Open Source license.  (And, EPL seems to lean toward industry.) For industry, it is like best of both the worlds. EPL is an OSI Approved License.
The EPL makes it easier for Industry to have proprietary systems based on Eclipse. (The terms of GPL conflict with the terms of EPL.)
Again, I am not legal expert. Please talk to your legal adviser for further clarifications.
An open source software can never survive without a dedicated strong technical development community. There is a strong active community of developers and vendors that always look forward to a better Eclipse day-by-day.
Eclipse itself is divided into many parts. e.g. CDT is the part that focuses on adding features for C/C++, JDT is for JAVA. Different people, either volunteers or sponsored by industry work on these parts.
You can find more about the different projects at http://www.eclipse.org/downloads/index_project.php
What does plugin based mean? The concept is easy to see, but difficult to explain in words.
With plugins, you can extend the functionality of Eclipse. E.g. the CDT plugin adds functionality for C/C++ Development. Pydev plugin helps for Python development. Developers have the flexibility to use a wide range of configuration management tools right within Eclipse. The plugins make it a feature rich offering.
More about plugins is described in detail in Plugins.
To see the wide variety of plugins available for Eclipse, refer to the The Eclipse Marketplace.
It works on Windows, Linux, Mac, etc. The look and feel is kept native. But the functionality remains the same.
We are not here for any flame wars.
If you already have made your mind that Eclipse is slow, there is nothing more to be done to convince you. But, it would be worth to see the Eclipse nightly builds page  . The performance of the plugins is monitored closely during these builds. This makes it easy for developer to notice that bug fixes do not add performance issues. It gives motivation to keep the builds fast.