Funny that you posted this, I just came back from their this past weekend camping with some family from East Texas.
Beautiful park! The restroom/shower by me was very clean but I can't say about the others. My cousins stayed in a cabin (site 405) that had power, water, air conditioning, and I believe heating and a small picnic table inside but no bedding; so air mattresses or cots. Me and my other cousin tent camped at site 334 which is right by the water. The cabin and screened shelters are great if you don't want to tent camp, plenty of space between units and all the sites were very well maintained. The loop I stayed at is mostly meant for RV'ers and were generously spaced between sites. The other sites are very close and on a very packed weekend (I think a Boy Scout Troop was visiting) I was glad we were not camping there. I think the park office didn't want us camping where we did so we were lucky to get it.
https://tpwd.texas.gov/publications/pwd ... 4_031c.pdf
I didn't fish but my relatives did and only one small fish was caught; take that for what it's worth. There are two sides of the park separated by Hwy 190, we stayed on the south side of the park. The fishing piers in both parks were broken but there is an observation bridge on the north side of the park that I saw plenty of people fishing off of. They also offer canoe rentals and I saw a few people fishing off of those (more on this later).
Pretty good trails for hiking (we were mountain biking) but my nephew came across a snake on the trail (I wasn't with him so I can't verify) and I'm pretty sure I came across a rattler while riding (I didn't see it but I heard it) but didn't stop to look :D Plenty of leaves on the trail so it would be pretty hard to spot them so be careful. We rode about 15 miles all together crossing over the highway from one side of the park to the other.
One thing I wish we had done was rent out a canoe and go paddling. We saw plenty of people of doing this and the park has canoe trails that are marked with buoys. And we missed signing up for this but they had a guided canoe tour the Saturday I was there that I wish we could have gone on. Just looked at their calendar and the next one isn't till 11/21.
One thing you might look into, if the park is booked or really crowded, is Sandy Creek Park which is south of Martin Dies State Park. We stumbled across it while riding and it didn't seem to be very crowded at all.
Not sure if this will be a problem now that the cooler weather has come in but the mosquitoes really came out in hordes once it got dark. Guess with the marsh/swap being right there it can get bad. I made the mistake of accidentally opening the door on my tent when I thought I had opened the window and it took me 30 minutes to kill off all the bugs that got into my tent.
And I guess the final thing is if you don't bring any firewood (or enough), they have stacks of it by the camp host that they sell for $5. Not sure how much you can get but it's by honor system. I brought enough firewood with me that I actually took almost half back home :)
I would go there again. Also there are a few camping sites in the National Forest near by that I would like to explore next time as well. I've got a few pictures I can share if you are interested. Let me know if you have any questions about anything else.