As with any published adventure, how creative it is largely depends on how creative the DM is. If all the DM is doing is flipping pages, then surprise surprise it's probably going to be a railroad. But letting players go off and do things that aren't in the published adventure is what distinguishes the good DMs from the mediocre.
Btw, I think a lot of people that just don't like Dragonlance use the whole railroading argument as a crutch to justify their distaste. If I had a nickel for everytime I've heard someone say, "Well you can't do that b/c the story doesn't happen that way..."
You can do whatever you (and your DM) want. If you choose to play a module verbatim as written, then it shouldn't come as a surprise when it ends up being a railroad.
And no, you don't have to play Sturm (
et al.).