It all depends on what you want to do and your level of expertise (somewhat) but more importantly, your willingness to read, learn, use search, test, and then do it all over again. We're finding that with Exile, the possibilities so far are seemingly endless (given A3 issues inherent in the game engine itself. Read on to learn about our voyage to where we are today.
We were one of the early A2 servers that was running an OverPochIns server. We customized it to our clan's liking and we ended up having a steady base of about 60 players with 30-35 active at almost any time day or night, most of which weren't our clan. I was primary modder and went to great lengths to fix the stupid things and make it somewhat more realistic. You weren't going to be able to pull a string of five DC3 planes with a bicycle, for example. You weren't going to be able to pull anything with a bicycle for that matter. Likewise for all vehicles. My tables were set so that you could tow a vehicle only with another vehicle that should be able to tow it. We had snap-to building. We had a roving band of three helis that circled the Tavi map just looking to start trouble. We had a fully customized Sector B that was hard as nails. All soldiers had the black SpecOps uniforms. We had machine guns on the walls as well as around the island. We had roving patrols. All were array driven so nothing was in the same spot on the next restart. We had bandit and hero missions... tailored so that it generally took cooperative play to complete them. Toward the end, we even had the latest Origins vehicles in there, including a fully functional submarine. Not to mention a lot of other smaller mods and scripts. And people loved it and started forming their own alliances. While it was indeed a PVP server, everything was customized (including zombies) to make it difficult to be a lone-wolf sniper picking off bambies. As things evolved and Tavi begun to disappear from the public's ability to modify, we tried all sorts of other things. Standalone - no one from our clan or group stuck it out. We tried it but it had too many bugs and deficiencies and very little means for us as server owners to address them.
So we tried A3. First with an Altis Life server. We found it took too much work and policing from the admins to make sure people followed their roles. But the roles were too artificial and when it was no longer enjoyable for the admins - we spent all our time babysitting - we killed it. We tried A3 Epoch because the A2 version was such a hit. But it fell short for the same reasons others have mentioned. So now we're on to Exile. Right now a Tanoa map and soon to also have an Esseker map. The Tanoa server isn't quite done yet but it is fully playable. Each time I add in a script or addon, I get it running error free and tuned to our liking before moving on. Yes we have Extended Base Mod (thanks Freakylein!) but I've customized it. Not all items are available and I've changed the respect and recipes for a lot of them. You aren't going to build an airport tower with two sandbags and three scrap metals (I exaggerate but we're getting closer to the original A2 Dayz feel - you need to scavenge). We have a really cool status bar (thanks Janski - we're still looking for an infection meter though) with ExAD. We have ExileZ 2 (thanks Patrix87). We went through great lengths to tune it. How many zombies spawn in at airports vs wilderness. How frequent are the waves, how aggressive are they? We tuned them so that if you are going to be a sniper picking off bambies, you are likely to have a zombie or two spawn near you and flush you out. You won't die from a single hit (usually) and they don't have a five-meter reach. If you're in a city, there'll be more of them. Airports and military areas? Even more zombies. We're running RZInfection (thanks DirtySanchez!) so you have a chance of getting infected. So you'd better find pills or an injector (or buy them from a trader). We're using Custom Vehicle Spawn (Thanks Warsheep!). We have boats that actually spawn around the shores (it IS a collection of islands, after all) and vehicles spawn near roads, airports (for the most part) just like you'd expect. But they're fairly sparse. You won't find a vehicle every few meters. Speaking of vehicles, none that spawn in are armed. And I have the CUP mods (thanks to the entire CUP team) so we also have some A2 vehicles and items. You'll see those A2 fishing boats spawning in, as well as Zodiacs. And they're along the shore! And the Datsun (Sundat?) pickup, as well as the random towing tractor and Skoda, to mention a few. I wanted to add the motorcycle but the physics are all messed up. And generally they'll all have some damage - very few are 100% repaired when they spawn in. We're running DMS (thanks Defent). We have missions. We're in the process of tailoring them as well - trying to foster cooperative play and make loot match the missions even more than they do already. We're working on tailoring the AI so they aren't aimbots, able to pick players off with one shot at 2000 yards. We're running Bigfoot's shipwrecks (thanks Bulleit) and so have shipwrecks. Now you can put that diving gear to even more use. There's even more but those are the big things. And of course there are the little things. To see yourself or your clan/family on the map, you need a GPS - a way to bring more usefulness to the GPS. If you have a shovel, you can bury a player body and a mound and cross appear. You default with your XM8 turned on when you log in.
I am planning on adding Extended Vehicle Repair (Thanks JohnO) in the near future as well as modifying the loot tables to include more of the A2 items. Right now if you find an A2 vehicle, the salvage trader doesn't offer anything. But I'm not changing it so that you're fully geared up within 10 minutes of landing. I'm also planning on adding the ability to hoist shipwreck crates onto boats. I'll also be building a Tanoa equivalent of Sector B, probably converting the one that is already part of DMS for a different map. Plus a few other things to foster cooperative play so PVP and PVE can co-exist (but PVP won't be easy) and bring even more realism and immersion.
So that being said, all the addon authors have gone to great lengths to allow a high degree of customization in their Exile addons and scripts. Not to mention that there's a lot of customization possible in Exile itself. I'm surprised more don't do so. Too many servers I've checked out just leave everything with the default settings. There's so much that can be done if server owners took the time to read, learn, test, adjust, re-test, etc. But I already said that!