To me the big improvement of the demo in comparison to the alpha is that you kill monsters faster, the alpha way of monsters hyper resistant that you needed to shoot for too long was just ruining the pace to me (and if you didn't found the damage increasing items, it was quickly becoming boring to spend several minutes killing 3 enemies in world 3).
But a bad point is that indeed the difficulty is way lowered, mostly because the enemies for some reason are even fewer than in the alpha (regular enemies, not the ones spawning by dozen when you open a portal), that's not much fun as the enemy should be more numerous if you can kill them faster to make the game more frantic.
Wouldn't be a problem if it was in the lowest difficulty level ( casual ), but it's unfortunately like this in normal difficulty. It seems the hardcore difficulty has the old spawn rate (though it spawns more advanced enemies)
But the main problem , that was worse in the alpha, is the repetition of the levels.
I completely agree they should have gone to the Spelunky route instead, with some more randomisation because in this state even if there are a few alternatives to some locations when you replay, playing again and again in the same places, same platform, etc ... that's just introducing boredom, never something good for an action game when it is one supposed to be very replayable
EDIT : just noticed there's a 1.0.1 version of the demo released
Risk of Rain Demo v1.0.1:
* Fixed a glitch where the difficulty would reset after beating the 2nd level
* Fixed a glitch where boss health did not scale correctly
* Fixed a glitch where the difficulty change on entering a level only lasted one minute
* Changed coefficients for health and damage scaling on enemies
* Changed coefficients on bonus spawns on late-game teleporter activations
edit 2 : just gave a quick try to 1.0.1 and it seems the monsters are spawning faster, unless it was just me "lucky" on that specific run, but it's better that way with the enemy dying faster than in alpha.