I'd consider myself a rather harsh critic, and I'm extremely pleased with the game.
Yeah, it's short (I finished it in a few hours while taking my time). But $25 for all 5 episodes, plus Puzzle Agent? Not a bad Christmas Eve present, and if you're a BTTF fan, don't waste your time waiting till February. I also got the free episode 1, and was annoyed...but it's worth buying now to put the impatience aside.
Yeah, it's also easy. There are a few interesting puzzles but none of them are too difficult to figure out. I think if you're new to adventure games, it'll be a decent set of challenges that will get you accustomed to what you're in store for. It's also got a somewhat unofficial hint system in that Marty tends to straight up ask advice through dialogue if he's stumped, or 'feels' he needs advice. So you have the official hint system, and this more unofficial one to assist to in a more natural manner.
The story fits in well with BTTF, even if a few bits seem overly cartoony. While there were some rather fantastical elements to the movies, it was all based on reality for the most part. That is the only gripe I have.
It would be nice if they eventually included the hoverboard and driving the Delorean, but I feel like it'd be tough given the movement system. It's a bit awkward, so adding in support for those two might be weird.
I'm frustrated that I'll have to wait till Feb to get the next bit of the story, but I believe they are definitely off to a great start.