Havarl is a unique planet in many ways. The subjective, aesthetic differences between Havarl and other planets are yours to quantify, but the gameplay differences on Havarl are worth noting. First and most obviously, Havarl has a tiny operational area compared to Eos and Voeld. This is expanded a bit by the fact that you can’t deploy the Nomad here - nor would it be terribly useful if you could, given the heavy vegetation and abundant Remnant structures. Speaking of which, the map is split into two unequal halves by a large Remnant trench running north/south, dividing the western two-thirds of the map from the eastern third.
While Havarl has no environmental hazards that’ll test your life support, the malfunctioning vault on this planet has led to another, arguably more annoying threat; hyper-mutated wildlife. The abundance of over-grown flora might make traversal a chore, it’s the fauna that’ll really hinder your progress. As you explore Havarl you’ll constantly find yourself pestered by various critters, including Drall, Creeper, Shemrys, Adhi, Challyrion, Galorn, Rylkor and Eiroch. Not only is wildlife more diverse on Havarl than any other planet, it’s far more abundant - expect to face larger groups of foes (especially roving packs of Challyrion) more frequently.
That’s not to say the wildlife on Havarl is the only threat you’ll face, as Remnant - ubiquitous throughout Heleus - are also present. As another divergence from the norm, you won’t find much in the way of Kett on this planet, but they’re replaced by the Roekaar, xenophobic Angaran rebels who don’t see much difference between Milky Way species and the Kett, and they’ll respond accordingly.
Since the Nomad isn’t an option on Havarl that obviously means you won’t be deploying probes and plundering Mining Zones. This isn’t to say there’s no mineral wealth on Havarl, though, but there’s far less variety, overall. Instead, as you explore be sure to keep an eye out for Nickel and Platinum nodes that are relatively abundant across Havarl. Also be on the look out for various scraps of Angaran technology you can scan and loot you can plunder - there’s a lot of history buried under the gluttonous vegetation on Havarl, and there’s no reason why you shouldn’t make a profit on it.
Finally, there’s something to be said about the quests on Havarl. There are relatively few of them, which is fitting given the planet’s size. Of the few that are on Havarl, a relatively high number of them are basically scavenger hunts, forcing you to find objects (both marked and unmarked) across Havarl. This is, naturally, best done as you see to other business. Speaking of which, it’s also worth noting that the main quest (and majority of the viability for Havarl) will come from the quest "A Dying Planet", which tasks you with getting Havarl’s vault back online. There’s no real reason to wait and delay this quest, as you’ll unlock more quests during and after it, and it’ll take you across the majority of Havarl’s operational zone, during which you can keep an eye out for the objectives of other quests.