I want to get across the point that I was no longer enthusiastic about something:
When I walked in the room I was disenthused by what I saw.
AFAIK, disenthused isn't a word.
Edit: Chasly was right about my question being more vague than I intended. Lots of great answers which can only be discriminated by criteria I failed to include in the original post. I will not repeat the mistake for future postings.
Thank you all for the help. I've marked the answer that best fits my situation as "accepted", but future Googlers should scroll through the list of answers for their needs.