Dungeons: they are decent enough and quite PUGable after they've been nerfed. Decent sets too.

New Currency: Tel Var stones are an interesting concept only found in IC. As you complete quests and kill enemies you'll start earning some stones. These can be used at the special merchants found in the Alliance sewer base. Their wares are most varied, from style stones to potions to soul gems, to Alchemy satchels stuffed full of nice flowers, Hakeijo runes and Seals of Retreat. The armorers provide some good gear and if you don't mind the gamble, buying the 3K Tel Var boxes with a random piece of gear has a decent chance at getting the Xivkyn polymorphs. You'll likely spend far less Tel Vars gambling for them than buying them directly. The random dropped ones can't be traded/sold though so there is that. The bad thing about Tel Var is that, even though the more you hold the more you'll earn, you will lose half of your stones each time you die. And those roaming bosses are extremely difficult to shake off if they happen to spot you down there.

Map: it's a bit of a nostalgic trip for those who played Oblivion, despite the obvious changes in layout and the sorry state the city is in. The sewers have many nooks and crannies to explore with books, skyshards, and a few interesting surprises. However the roaming banner bosses are a major pain if you run into one by mistake, so it requires one to be constantly aware of the surroundings if you're alone and just exploring. The city bosses are challenging as well.

The Quests: they can be quite interesting, with good NPCs. However there's a couple of them which are not as easy to solo as the regular PvE content. Add this to the fact that you may wander into a boss or members of the opposite factions while running from point to point completing objectives and they can become very frustrating. Definitely worth doing though, if only for the dye and the achievements.

Centrata Event: the center area of the sewers provides a very unique event with equally unique rewards. Completing it awards a nice dye, but the fight is going to be nigh impossible to solo even to the best players, so you definitely need a small group to tackle it. The 'rare' drops from the boss are a carrot dangling in a mile long stick. We all know they are there. They are enticing. But the fact that only 12 people get loot regardless of how many are in the group, and the droprate of the things which people are actually interested in is probably 1% or lower, can be a letdown. Alkahest and a single key shard are 'trash' rewards for such a spectacular and challenging event. Hakeijo runes can drop and they're not that rare. The pet also has a decent drop rate. But the skin, it'll be far easier to farm the gold and buy the box from another player, unless you're one of those incredibly lucky to have it drop.

PvEvP: this is probably the most controversial of the aspects. There are plenty of PvE quests and daily objectives to fulfil in IC. However seeing as it's an area with PvP unlocked it means PvErs will run the risk of being constantly attacked while working on their objectives. This can be very detrimental for the experience because a) it keeps players on edge and constantly having to fear being attacked out of nowhere by a ganker or steamrolled by farming groups, b) you'll be forced to spawn at the base, and depending on the quest that may mean crossing the area all over again to talk to an NPC, while trying to avoid the exact same people who killed you just now, and C) (this is the one I personally find the most aggravating) your stash of Tel Var stones will be STOLEN by the player/s who killed you, meaning you'll spawn with 50% less than you had before dying. Not just lost as when you die to an NPC/boss. This serves to promote PvPing/ganking and is the reason why so many people hate that place.

However as it's been mentioned before, most of the times the IC is pretty empty. Why is this? Because it calls little to both PvPers and PvErs alike. PvErs avoid it because they don't want to deal with rhe PvP aspect of it while playing. And the PvPers also prefer Cyrodiil/BGs because pickings are generally slim in IC.

Is it worth it? That's up to the player to say. Test it with ESO+ and decide for yourself.

I use to like IC once i got use to the fact that theres a ganker everywhere.

It's a mess of a dlc that is dead 99.5% of the year.