I could go through a ton of things about Missoula and Montana you would miss when you leave. There are a lot but keeping it more specific to Missoula. 

1. The Mo-club burger, the all time greasy hole in the wall delicious burger. I'm sure other places you visit have this same type of place with a great burger but it takes you so long to find out that local info plus

2. Hiking the M and seeing the Valley

3. The crazy events, from the Naked Bike Ride, Vintage Bike ride and day of the dead festivities this town really has some fun different events.

4. Local sporting game support here is fantastic, from the Griz games to the Maulers to the Osprey, there is a lot of fun to be had with local sports in Missoula.

5. Of course for me....fly fishing would be the big one, I could be somewhere you can still fly fish but it would never be like fly fishing in Montana.