Wow, what a blast from the past! Overall I found it quite impressive and smooth to play: I loved the fresh coat of paint over everything that makes it more readable and pretty, and I loved the cool additions like new boss fights, new point-n-click puzzles, charming voice acting, remixes to boss mechanics, and so on!
I do have to say, though, that as much as I like it in general, there were some more questionable design decisions that make it a bit of a lesser game than the original for me.
For one, I found it really odd I couldn't hold down the trigger to keep firing the machine gun like you could in the original: having to tap fire each shot not only is illogical, but it really wears down my old man hands. Tap fire makes sense for the shotgun, sure (which I had no idea how to switch to manually), but for the machine gun, I wish I could hold it down.
While I do like a lot of the additional bosses and changes to some of their mechanics, some of them were worse overall for me. I didn't like how you couldn't skillfully shoot the grenades out of the air anymore like you could before in the first boss fight, I didn't like how the attack telegraphs for the grenade rolling down the stair were behind the player making them difficult to see, I didn't like the awkward spawning for the bear duo boss where sometimes the minion would instantly respawn giving you no time to shoot the main bear at all, and so on and so forth.
But the biggest one for me was the inclusion of the point-n-click adventure parts: don't get me wrong, I like me a point-n-click, but when you combine it with the hard difficulty boss fights and fact that death means starting all over, it can get really monotonous to redo those sections over and over again: the original was just a boss gauntlet so it didn't have this unnecessary busy work. Yes, you get a few lives to ease the pain, but really, I almost feel like the game should just have infinite lives instead of relying on this awkward half-measure.
Also the hint system was really silly and pointless: it gave me a hint on how to beat the shadow boss when I was already way past that, haha!
Again, I have to reiterate that as much as that is a big block of text right there complaining about everything, I still did overall have a ton of fun with this and, no matter how much I died, I never wanted to quit, I wanted to get right back in there to see what craziness happens next! Just, uh, let me rest my carpal tunnel for a sec...