If Zion were a pop up book...
Difficulty level is a tricky thing for Fallout NV due to the fact that you can change it. In addition, there are three possible companions one of which you can have at a given time throughout the entire DLC. I played on "very hard" without companions save to hear their dialogue and meet their characters. I was leveled 22-25 and wore reinforced leather armor for near entirety. I found the Zion mantises, giant cazadores, and spore carriers to be particularly challenging and, under similar conditions to my own, you can expect them all to kill you in .5-5 seconds if you're at all ill-prepared for the encounter. I, for one, quite enjoyed that! The exception to my enjoyment would have to be the unfairly high perception of cazadores. 80 sneak level seems pretty darn good, right? Well, I was sneaking around in the dead of night and hear the cazadore poison sound. There is a glitch in the game where if anything is stung by these winged devils in your vicinity, you hear the sound as if you were poisoned. This glitch is now a blessing, serving as an alarm. I can't see a red indicator for the hellish insect so I sneak off to the nearest shadows, pull out my riot shotgun and wait- no movement. The red indicator pops up and soon after I hear its damned wings humming the tune of evil. As soon as it came into view I lost my hidden status and despite the 1,000 rounds I let out of that shotgun I was dead in two strikes. They're lightning fast and can pop up out of nowhere. Sometimes, when you cripple their wings, they still fly around as if they had just come from Scarface's house. The "and stay back" perk in addition to "silent running" helped.
I would like to call the next section, "New Stuff." If you've played Fallout 3, there are no new animals as the yao guai is the only animal included in the DLC that can't be found in the Mojave. Now, they come in a variety from cub to...well I won't spoil it. Geckos are seen again, now in the green option. You can shrug off their spit until they poison you with their bite. Giant mantises are now ZION giant mantises and if they get you, you're got.
The additions to crafting are fairly significant. My personal favorite is the gecko-backed, reinforced leather armor which adds 5DT and poison, radiation, and fire resistances to the arguably most aesthetically attractive armor in the game. And, I felt rather appreciative of "blood shield," a craftable medicine that boosts your poison resistance.
There are enough new and unique weapons added to hook you into buying the DLC. The new perks are, for the most part, useful for character building- particularly for the survivalist aspect. There is one perk with broad appeal: "Grunt," which gives a boost to some select weapons and in addition to the cowboy perk, which makes Chance's knife kinda the bomb in my opinion.
I felt that the story, while interesting, was a hurt a bit by its "fetch" nature. I was, perhaps wrongfully, comparing it to Point Lookout of Fallout 3. There are enough similarities for that to be fair, though. It's an open-world oriented add-on. The enemies are more difficult. There's even a quest where you have to get high and undergo a test to prove your tribal worth. But, these components were more skillfully integrated in PL, and the story benefited. That said, I did feel for the natives, especially the sorrows. Joshua Graham was a tastefully strong character with a great historical backdrop. The religious themes brought poignancy to the story. And, the diaries of "The Father" affected me a good deal and I relished approaching a new terminal to find out more, if my legs weren't crippled by the time I got there.