Unfortunately, it does get quite laggy, and some quests keep getting glitched and become impossible to complete. It takes a long time to download, and takes up alot of space (between 2 and 3 gigabytes). When you have this open, it will also make any other programmes you have open lag too, and their server maintenance updates stop you from accessing it for a few hours most weeks, although this is to make the game better.
In reality, to complete the game you are most likely going to want to spend some real life money to buy things from the "Item shop" else it will take you a very long time to complete and max all skills and get the best armour you can. Quite a few features are difficult to understand and quite awkward, things like the "Arcane Transmutor" are difficult to get the hang of, and the dual class system can be awkward to follow, many will find it difficult to train their secondary class well having done most the low levelled quests on their primary.
I have covered most of the review parts in "The Good" and "The Bad" all i have to say is, try it, its a great game and free, if you dont like it just uninstall it.
I gave the game a 4.1 because it is a fantastic game, it will keep you entertained for hours, however there are still problems with it that will hopefully be fixed in the near future.