The $15 parking price is pretty much universal, except at Kentucky Kingdom, which does not own its parking lot (the Commonwealth of Kentucky does, and the last time I was there it was five dollars, still).
I have found Six Flags America and Six Flags Great Adventure to have made improvements comparable to those in Georgia, in guest services, cleanliness and staffing. I also found Six Flags Kentucky Kingdom, though not quite rising to that level, to be much improved.
I wish I could say the same about Six Flags Over Texas. I can't. I was there a week ago last Sunday and Monday. The food places were mostly closed. Those that were open were very slow. One train on most all the coasters. Only two shows on Sunday, and NONE on Monday. No trams in the parking lot. And the park itself was not very clean. The parade at the end of the evening was among the shortest I have ever seen, and the employees participating in it looked to be glum and unenthusiastic. It was if a pall hang over the park. The SFOT I remember under the old Six Flags was much better than this. Something is wrong down there, or at least was the two days I visited.
That being said, Mr. Freeze is running awesome (even though it seems to not open with the park), and Shockwave was giving Mindbender a run for its money for the title of best grand old Schwarzkoph...