Hi there! We lived in Austin for 7+ years, and I agree that the heat is hard to get used to. (I'm from the mid-atlantic, I really couldn't get used to it.) The last summer I spent there we had over 90 days in a row with temps over 100 (105's, 106's, with heat index in the 112's, etc.. )
November and March are the nicest months, but another Fall difference I haven't seen mentioned is that the trees do not change colors in Austin. Maybe a few do, but in general, there is no color change. I really really missed this.
The closest clean beach is South Padre (a 7 hour drive, if I'm remembering correctly). We went to Corpus Christi once and there were signs on the beach with directions on how to remove oil residues from your body. Gross.
Tubing (or toobing, as some put it) down the Comal and other rivers is really beautiful. Not sure how the drought affected this activity, since I moved away from Austin more than 2 years ago. But the drought is another big thing to consider. Rarely ever having rain was kinda depressing for me.
The Hill Country is nice, but as others said, there are absolutely no mountains. San Antonio's River Walk is a nice day trip, only 1.5 hours away.. Dallas and Houston have a lot to offer. But like others have said, it's pretty land-locked and far from any non-Texas places.
Positive things about Austin - people are really nice, jobs seemed plentiful when I was there, at least in high-tech industries. Great food - all kinds. I miss breakfast tacos!
North Austin is close to a lot of major employers, and is cheaper than downtown or central Austin. We rented a 3 BR / 2 Bath HOUSE there with a private yard, a pool and playground in the community, 5 minutes from work, 5 minutes from Whole Foods and shopping, 20 minutes to downtown (at night, no traffic) for only $1300/month. This is crazy to me now, considering we currently have to pay $1750 for a smaller 3 BR APARTMENT with no community features at all, in Maryland. North Austin also has the best, more authentic Indian food in Austin. I miss that, too. Yum. Anyway, Austin may be more expensive than the Triangle, but it's still cheaper than CA.
So in MD, we now we have 4 beautiful seasons, as well as beaches and mountains and other cities nearby. We've been thinking about the Triangle, too. Have visited the area, and have have more visits already planned. We really liked it, because it seems to have a lot of the things we love about Maryland, but a better cost of living / quality of life. And the jobs in our industries seem healthy, too.