Feature extraction for sentiment analysis
Have a look at these papers-


Semantic Similarity - 1
Semantic Similarity - 2


They came up with a good solution. Have a look maybe you will find something of your use in it. Plus try exploring these too


vaderSentiment 0.5
(VADER Sentiment Analysis. VADER (Valence Aware Dictionary and sEntiment Reasoner) is a lexicon and rule-based sentiment analysis tool that is specifically attuned to sentiments expressed in social media, and works well on texts from other domains.)
Demo- Sentiment Analysis with Python
(This is a demonstration of sentiment analysis using a NLTK 2.0.4 powered text classification process. It can tell you whether it thinks the text you enter below expresses positive sentiment, negative sentiment, or if it's neutral. Using hierarchical classification, neutrality is determined first, and sentiment polarity is determined second, but only if the text is not neutral.)


Hope it helps! :)