I'm not a regular Supernatural watcher, but I also noticed that this episode played with the idea of alternate dimensions in other small, nuanced ways. In particular, Sam and Dean don't drive an Impala in this reality. That and other small touches make us aware we've slipped into another universe. I appreciated the attention to detail, and I'm sure that for longtime watchers, the episode's meticulous attention to continuity paid off richly.
Also, isn't it a wee bit disingenuous for the writers here to go after Titanic tooth-and-nail, while crafting, essentially, a total knock-off of Final Destination? There's a cognitive disconnect between a show that bashes Titanic as a bad movie while at the same time it so knowingly and enthusiastically rips off another popular movie. If you want to prove that Titanic was creatively bankrupt, showcasing a creatively bankrupt rip-off doesn't exactly make the case that your production is better. But anyway, according to Supernatural, Titanic really, really sucked. By inference, I guess that means that Supernatural is totally awesome.