I'd say the odds are 50/50. Actually, I put the odds of a shutdown at about 55%. There's certainly enough substance here to be wary.
The government could shut down because of disagreements over defense spending, funding for Trump's wall with Mexico, deportation of illegal immigrants brought to the U.S. as children (the "Dreamer Act" also referred to as "DACA"), funding for Planned Parenthood, funding for Obamacare (called "SCHIP"), disaster relief and more.
There's not much middle ground between Democrats and Republicans on many of these hot button issues.