It depends on who you ask. It
WAS a negative word meaning a person who has no life that is way too into anime and manga but I like to believe we pulled a yankie doodle dandy on that shit in the US so now to me
Otaku = someone who likes anime and/or manga beyond the casual watcher ...... not that there is anything wrong with watching anime casually. It just seems easier to say "I am an Otaku" rather than "I am really into anime/manga/ect ect ect (vocaloids, figurines conventions, cosplay)" it kind of differs from person to person so I would be an "Anime Otaku" since I have favorite characters, genres, VA's (Voice actors for the US or some people like to call them seiyuu for Japanese subs), and generally spend a lot of time thinking about anime.
I'd like to think the negative connotation is gone but it isn't ............ yet
There is also something called a weeaboo which is a
WHOLE NOTHER TOPIC LOL ..... that one I think will always have a negative connotation to it. The gist of it is "I watch anime/read manga thus I know everything about Japan" .... the lines between Otaku and weeaboo can sometimes blur but I'd like to think of myself as an "Otaku" and not a "weeaboo" since I don't love every single thing about Japan ... I just like their anime. .... maybe too much but meh, whatever.
These are all my personal opinions but I kind of think they are good ones