What are USMC infantry deployments to Afghanistan like?

Aside from being bored, exhausted, frustrated and uncomfortable most of the time, you can also expect to be hungry, dirty, and not know much about what's going on. It's not all Fallujah and Marjah, even those two had a lot of the above listed things.
You can also expect to be very well trained to handle anything that comes your way and led by some incredible Americans. You'll hit the highest of highs and the lowest of lows. Oh yeah, and you MIGHT even get to do a little shooting.

If it's anything like the Army infantry it can be summed up with days on days of boredom, accented by moments of sheer terror.

Talking to Marines that have experience is best. Documentaries can help, if they are honest, but many are fluff and PR. Search for USMC documentaries and weed them out. Here's one from 2011 of G/2/5 and is worth a look. The Company Cmdr in this was later a recipient of the Leftwich Trophy for Outstanding Leadership, so he has his stuff wired. A Mustang and West Point grad. There was another from Iraq but I don't remember description. It had some good input from the BN Marine Gunner and others. It was in the zone and had live-fire segments. The most intense engagements like Fallujah likely won't have any footage and there are many different types. House to house, high-intensity, counter-insurgency and more, so don't use this as an example solely. Any deployment is tough. Hope this helps.

http://www.documentarytube.com/videos/marines-in-afghanistan-the-untold-stories-of-the-5th-marine-regiment

https://www.mca-marines.org/news/maj-benjamin-middendorf-honored-prestigious-leftwich-trophy