Its really quite excellent - I'm glad it came to Steam. I am unsure if the Steam version has anything that the X360 version doesn't, but I'm always happy to support a PC version of a formerly console-only title, provided it is a good port; This one is. Gamepad support is great, at least if you have or emulate a XInput (ie X360) pad.
One thing I'm really, really happy with is the checkpoints. In a game like this, when I'm trying to ensure I get the highest rank, find all the collectable scrolls, and complete all the challenges in a level, I'm going to have to retry - a lot. Many titles would make you go back to sparse checkpoints, or perhaps deny you the ability to successfully complete that challenge unless you restarted the entire level, but thankfully Mark doesn't do that. Go to the pause menu, hit return to checkpoint, and you'll be sent back between 30 sec to 5 min worth of gameplay and you'll get to attempt that last gambit again. Major bonus points in my book for providing this feature. For instance, early on there's an optional objective to make it from a certain checkpoint to the inside of a generator room within 1 minute. This happens in the middle of a mission so to speak. The first couple times my haste got me detected, so I was thankful to return to checkpoint and try again, completing the objective.
Oh, and thanks to its animation and design, it is probably the closest thing we'll see to a recent "Samurai Jack" game