The game is a beta, so first thing I will express is that there are bugs, but like all bugs in a beta, they will eventually be squashed.
The largest bug I came across was the whole getting locked and stuck in a location/window when talking to someone or interacting with something, ie camp fire or crafting tool. I didn't realize that you could resolve this by using the /reloadui command until many hours into the game unfortunately.
I never experienced lag or any other misc network related issues.
The graphics are simply beautiful and the scenery is astounding!
The level of detail on the objects and characters is mind blowing and shows just how much work the devs have put into the game. I've heard some people complaining that the texture level isn't that good, but to me on all maxed out settings it seems great, but being a beta the Devs most likely only have a single texture pack loaded. After release there may be an add-on option for additional higher quality texture packs, so I wouldn't fret over it.
I've heard people complain about the lack of interactive objects in the world, well that's something they can work on, but I realize that the task of keeping track of all the objects in the game across every client at all times might be a daunting task for the devs and one where resources are simply not available. Then again it might just be the beta...
My actual biggest area of concern of all the possible issues I've seen or heard about is the inventory. It is the one single are of the game that has the most impact on my playtime and enjoyability. The devs went for a slot based inventory instead of a weight based one. This creates an issue where a single flower takes the same space as a piece of armor, which is ridiculous to say the least. My underlining point is that this system of inventory makes me have to spend far too much time having to run back and forth to sell; if I wasn't a crafter then perhaps that wouldn't be so bad, but I, along with many others are.
This would be easy to fix if an alternative bag was added to the system specifically for harvested ingredients such a plants, another for fishing supplies, etc, or they could simply just set the inventory to a weight limit like previous Elder Scrolls used, though I think implementing that might be too late into development to perform.
ChipDancer