yea, texas weather can get kinda shady sometimes. it'll go from 95 to like 45-50 in a matter of hours. and there aren't ever "light sprinkles," always giant rainstorms
as far as the austin area, i lived in a suburb of austin for 5 years before college and it was a pretty nice area. the nightlife is pretty cool, ideal for college party-goers and artsy types. plus, there are all the political things going on (since it's the capital)
the only downsides of austin are 1) size of the city and 2) size of the school. 1) once you've had your fill of the area, you're pretty much stuck unless you want to make the drive to one of the bigger cities (S.A. = about 2 hours, DFW = 3-3.5 hours, Houston = 3-4 hours). 2) UT is HUGE. lots of students on a small campus. and don't let me get started on I-35 traffic in austin

texas state is smaller than texas, but still pretty big with 20,000+ students.
from what i understand, the greek system in austin is big but not all that. and i haven't really heard anything about texas state's greek system.
i go to UT-Arlington (dallas area) which is also a big school (25,000+) and an ok greek system. we have 28 GLOs, but none have massive enrollment, so i guess you could say we're kind of close knit. SMU (dallas) and TCU (fort worth) are another story. the greek systems pretty much dominate at those schools.
i think being a greek in texas is fun. there are dozens of schools (most of which are within driving distanct) that have greek systems, so you'll always be meeting new brothers/sisters, which is always fun