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This is from the point of view of a first time user, testing different platforms for reliability.
My biggest problem in Vanilla is with plugins, which are not treated as core functionality.
2.3 had a large preinstalled set of plugins which covered a lot of essential areas (e.g. gamification).
It is a common assumption, that all parts of an official release, including plugins, are certified to work with the new build.
Now, 2.5.1 includes a much smaller set of plugins, practically removing a lot of functionality (like YADA).
Yes, they can be installed, but they can't be trusted to work with the latest build.
This creates a perception, that Vanilla's feature set is restricted to its core functions, and every extension can be broken in a future release. It doesn't give much confidence in using any of the extensions.
The obvious justification is that updating plugins is responsibility of their creators, but I would argue that those included with a build should have a special, protected status, and should be treated as a part of a modular core functionality.