A little soft
The big additions in Hard Reset Redux from the initial 2011 release are readjusted enemy spawns and damage, infinite sprinting, quick dashes, and a katana.
The new enemy spawns and stats are much easier than before. Enemies as a whole hit softer and have less health, and many of the encounters have less going on (though there are a lot more flying enemies). "Insane" mode in Redux (the hardest difficulty before the beat-it-in-one-go Heroic mode) is probably the same difficulty as Hard in the original, or maybe even easier than that if you're judicious with the sprinting and dashes.
Much of the difficulty in the original game was through how limited the player's movement is, making it easy to get boxed in by swarms of enemies or constantly pegged by projectiles. It was a more methodical shooter than many gave it credit for, and it rewarded planning over raw reflexes. Redux's infinite sprint and new dashes a la Shadow Warrior makes that almost completely moot. It's now possible to dash circles around enemies and dodge just about everything, making combat feel much faster and reflexive (especially with the katana), but also undeniably easier.
The katana is introduced about three or four levels in, and it's pretty much a simplified version of Shadow Warrior's - left click to swing, right click to hold for a harder swing. Redux's dismemberment system is less visceral than SW's, and the fact that the sword is so basic and has no upgrades like the guns means that there's no need to ever use it, so it's really just a novelty. I enjoyed softening up crowds of enemies and then jumping in to slice them to pieces, but it's still probably more efficient to just gun them down. There's a new "zombie" enemy essentially designed for the sword, but they're extremely weak and barely even attempt to attack, which is perhaps telling of the sword's usefulness otherwise.
Someone described Redux as "Hard Reset with a Shadow Warrior mod," and that's a pretty good summary. I would probably recommend Redux only to people who really liked Shadow Warrior or couldn't get into the original Hard Reset. I enjoyed it a lot, but I also loved SW and considered HR to be just good. If you are someone who sincerely thinks HR was a great game, Redux will probably be a letdown.
If this would be your first go-around with Hard Reset, however, I'd recommend you give the original version a shot first. If you end up getting too frustrated with it, then give Redux a go - it might be right up your alley. On the other hand, if the original HR clicks with you, then only look at Redux if you're interested to see what a faster, easier version feels like.
(A side note: After beating Redux, I went back to the original and played it on "Insane", and l ended up enjoying it much more than I did before, and maybe even more than Redux itself. Of course, that's just me.)