Like Dangerzone stated, the difficulty of the episodes in any given Telltale season stays pretty much the same throughout.
However, I have a feeling that things will be different this time.
Sam & Max and Tales of Monkey Island could afford to be a bit more difficult than Back to the Future, because the target audience for those games is mostly made up of adventure gamers who grew up on LucasArts and Sierra's point-and-click games.
However, with Back to the Future, Telltale has a chance to reach a much bigger audience, a lot of which probably never played a point-and-click adventure game before and the last thing they want to do is antagonize that audience by making a game that will not let them in.
Telltale's games have never been the most difficult, but if you search the Telltale forums, you will find out that even their easier games from other series provide some challenge to players who are new to the point-and-click adventure world.
I predict that the difficulty will increase gradually over the course of the season, possibly reaching a TOMI level (but probably - hopefully? - not a Sam & Max Hit the Road level) by the last episode.
I actually believe that the reason that Telltale is not going to make the free episode available before February is that they want the people who might decide to give up after one episode because it's too easy, to check out the forums (maybe to post negative comments about the lack of difficulty of the game

) and see comments made by people who played the second episode and might have found the difficulty nicely increased.
It's all speculation at this time, but that's what I'm really hoping for.
As for this:
Quote:
Originally Posted by Dangerzone
The best way to see for yourself is to simply play another telltale game season :P
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you might want to try a free episode, say
this one, which might give you a better idea of the usual difficulty of Telltale's games.