Yeah I think the difficulty, or lack thereof, is one of the reasons why Act 1 feels so quick. I played through the entire thing in 3 sittings, but I could have done it in 2 if I wanted. The first time I launched the game, I blew through Shay's entire scenario in 90 mins, in a single sitting. I wouldn't say that I was never challenged at all, because there were a couple of puzzles which required some logical thought, but it also didn't really stump me. There are also some puzzles which might require backtracking if you missed a room or an item required to proceed. But other than that it was pretty much a breeze.
Vella's story actually felt like it had more old school adventure elements to it, with a lot more dialogue and characters, and some dialogue "puzzles" too. But again, there's nothing which really stumped me much because it seemed fairly obvious, and picking every option available and grabbing every item you can take as you go along is pretty much the way to go. I actually think the puzzles for Shay were more clever, while Vella gets to explore a more interesting setting with more variety in tone.
Overall though, I think even if this is half of the entire game, the size isn't particularly small, it's just that it feels light in content in terms of population and play time. I counted the number of unique screen areas (most of them scroll though, so they're larger than one actual "screen"), and Vella has about 18 screens, while Shay has about 19.
Almost 40 unique screens with something to do and interact with in pretty much every screen, and everything being fully voiced, is honestly not bad in terms of design for half an adventure game, especially when the story and characters are fairly unique and doesn't feel remotely derivative. Yet blowing through it in just 2-3 sittings taking up 3 hours definitely does feel short.
One thing I hope for is that since it's likely the second half of the game will reuse many of the areas already created for Act 1, they can maybe populate them with new content and puzzles without having to create tons of new assets. That could definitely increase the amount of game there is without increasing the budget that much... maybe?
I really enjoyed what there is so far. I just wish there were more of it!