I'm about halfway through the endgame, and I haven't experienced any game breaking bugs so far, except the occasional crash or a dungeon that cannot be completed.
But I do have my concerns. The obvious issues of build diversity and broken passives. There is no real point playing anything except bleeding edge right now. Well, you can, but it's like playing MM instead of BM right now. You can do it, but the results are underwhelming. And that spells are not even remotely competitive in the end game. The game feels like it never really left the early access, and the weekly patching cycle does nothing to alleviate that feeling.
Then there are the broken mechanics. Like gold drops being useless from level 10 and up, magic find on gear doing nothing, expeditions (follower missions) bringing in better rewards from "partially failed" results over "success" ones, crafting buildings locking you out of the game, iffy collision and pathing, explosive barrels damage being unmitigable and becoming the biggest enemy in the end game...
And then you have the division 2 loot syndrome. Maybe there are players that enjoy going through several inventories of loot without ever seeing even a usable item, much less a marginal upgrade, but it rubs me the wrong way. It gets better when you start getting reliable legendaries and unlock the high end crafting options, but it's a long way to that from the campaign end. And uniques being uniquely trash does not help.
All in all the game reeks of either negligence or incompetence, not sure which is worse. It obviously should not have released in this state. If it wasn't for extra long January drought this year, it would of already been forgotten by the majority of the players. But they got lucky with that, so now the devs need to get their asses in to gear and get it to a good state before things like doom and mount&blade release, or they might never have server capacity issues ever again. There is also division 2 expansion that might pull players away before that, but I don't really have confidence in that game any more.
And all that is a real shame, because the game has a lot of potential, and we need more players in this area, since aRPG fans have nothing to play long term but PoE, and looter players are stuck between disappointments that div 2 and destiny 2 are. At least there is still good old reliable warframe, if you don't mind taking a semester to learn the basics.