In general, the Evangelion mangas are considered good. They expand on the anime's universe, providing more depth and character development. However, it depends on personal preferences as some might find the style or pacing not to their liking.
Perhaps. The Evangelion fandom is known for its active participation in creating and consuming fan works. 'evangelion the one i love is fanfiction' could be popular if it manages to resonate with the fans' emotions and expectations. For example, if it delves deep into the complex psychological aspects of the characters, similar to the original series, it might gain a following. Also, if it provides a fresh perspective on the love stories within the Evangelion universe, it could attract a lot of readers.
Legally, it can cause problems for the franchise. Since it uses the Evangelion name and concepts without proper authorization in an inappropriate context, it could potentially lead to copyright issues. Also, it can limit the creative direction of the official franchise. If the public perception is skewed by this inappropriate fan fiction, it may be difficult for the official creators to explore new and positive storylines and expansions without first having to disassociate from the negative connotations created by the erotic fan fiction.