There are several new game modes that have been added since launch like Underground, Incursions, Last Stand (though this mode doesn't require end game equipment), as well as new Dark Zone areas, Global Events and Legendary tier missions. A lot of changes have been made to the equipment system (most significantly gear score and equipment sets), expanding the endgame loot hunt a bit further. Once you hit the level cap you now also get caches of armor, phoenix credits, and/or weapons upon 'level up' (i..e after getting a set amount of exp). They also added High Value Targets to PvE, which are basically named mobs that are far stronger than those normally walking around the map and involve defeating a few waves of enemies within a set amount of time to 'lure' them out. Dunno at what point you quit, but they added a lot more daily/weekly objectives beyond just the daily/weekly missions.
Underground allows you to play through missions that have randomized levels and objectives to which you can add modifiers to get better drops. I personally really liked it, but it hasn't been very active and as a result I haven't put that much time into it. There are some changes to it coming up in 1.8, but I dunno if that'll bring people back to it (I hope it will!). Incursions and legendary tier missions are significantly more difficult than the challenging tier without making enemies more bulletspongey (regular mobs anyway, the bosses are still pretty tanky). They're really fun to play through imo and require (near) endgame equipment. Last Stand is a survival mode. I haven't played it myself so I can't comment on that.
So it's a lot easier to get endgame gear and there's more variety in the means to get it. I'm not a huge fan of the Dark Zone either, so I got everything by running missions every now and then, exploring the map, finding collectibles, defeating bosses, doing HVTs, etc. Only exotic tier stuff is kinda hard to find, but there are a number of surefire ways to get them through weeklies, incursions, etc. Since I hit what I felt was a sweet spot in my build I've been doing legendary missions and incursions, which are a nice challenge imo. Preferably played with a group I imagine, but I've only played it with randoms and most are competent enough to finish the quests.
The 1.8 patch is gonna add a new PvE zone, a new (non DZ) PVP mode, and a bunch of other stuff. Looks pretty promising. Also, free!