Is this bag actually waterproof?

The shell is listed as waterproof, so it handles rain and spills. Zippers and seams are usually the weak points on bags like this, so don't submerge it or trust it for hours in heavy rain.

How much gear does the square duffel hold?

The square shape gives a boxy main compartment that fits gym clothes, shoes and a towel, or a couple of days of clothing. It is a carry bag, not a week-long travel bag.

Does it have a shoe compartment or separate pockets?

No. It is essentially one large compartment, so pack shoes in a separate bag or use packing cubes if you want separation.

Can I carry it on a plane?

It works as a personal item or short-trip carry-on if you pack light, but check your airline's size limits first. There are no wheels, so you carry it by the handles.

Is it only for UConn fans?

The graphics are UConn Huskies branding, so it is aimed at fans and alumni. Non-fans can still use it as a plain blue duffel, but the team marks are prominent.