Your entrance is pretty good but doesn't look Six Flag-ish.
This is what I mean. You have the basic structures, but when you title your park as "Six Flags", you must make your park have a six flag-ish atmosphere.
So, look at actual six flags parks, use some of their ideas, and expand on them. for example, let's take a look at your entrance, ok it looks like an entrance . . . and that's it. But now, let's make it more six flags - like. Take a look at . . .let's say, SFoG's entrance:
http://www.danaleigh...t.com/wpe20.jpg[/url] (or just any other SF entrance)
take a look at the textures, walls, and the overall structure. Now, use what youve learned from tht and expand on it, throw your own ideas in there. and tada, you have an entrance that you'd expect to find in a SF park.
Basically, what im trying to say is you cant slap a brand name on a park, you have to make your park "be" that kind of park (whether it be SF, Busch, Disney,etc.)