I like Reimers, but it is kind of two-faced. If you do the entire loop (follow the black trails) it's about 11 miles. The first 6-7 miles is fun, climby, techy stuff. The rest is flat, windy and meandering which I usually just want to end. It's only a 30 minute drive from my place, and I like the park so I hit it every now and then. And there is little shade. But I go to Pedernales Falls 2-3x as much, and it's another 10-15 mins.
However - they just built this new downhill trail which they call the Flow Trail. Not sure why they call it that because it is more of a jump trail and is much gnarlier than I was expecting. It has doubles, tables, gap jumps, drops, and a large hip jump near the end. There are 3 features that are signed as double black with signed blue B lines. 2 of them have high penalty for failure (I went ahead and skipped those). It was a bit surprising to see a trail like that pop up in a Travis County park. Kudos to whomever made it happen.