I'd like to start out this review by explaining one of the most important things to understand about this game. It's free to play, and it has microtransactions, but Grinding Gear Games does not get greedy at all. It is impossible to purchase an item with stats only cosmetic reskins of the things you already get. They sell additional storage space and character slots, but they are already very generous with the amount they give you.

I loved this game from the start, but I have waited to review until I could experience end game content and multiple characters to have a good understanding of the game. One of the nice things about this game is that it was designed by and for hardcore gamers. The game can be a bit slow for the first 30 minutes or so, but by the time you get to act 2 it get's a bit more fun. With every act you move on the challenge will be ramped up, and after completing all three acts(act 4 some day), you'll move on to the next difficulty. The final difficulty, merciless is very difficult, but not uncompletable.

Some nice features to the game would be that the skill system is highly customizable, and all kinds of crazy builds are possible with it. One of the recent featured build of the weak involved throwing traps that once triggered would shoot burning arrows, and then the burn status effect would spread dealing high damage to everything on the screen. the way the skill system works is that gear you wear has sockets that you can put skill gems in. If the sockets are linked, you can link support gems with skill gems to make custom abilities. There is a skill tree too, but it deals exclusively with passive abilities. The skill tree is huge and daunting, and it's usually reccomended to find a build on the forum until you get a better grasp on game mechanics. I recently designed a build and have got it to the start of act 1 merciless, so far it's doing well.

Also worth noting is that the crafting system and currency system are intertwined with one another. As you play you will accumulate various orbs that can be used to modify equipment. A chromatic orb would re-roll gem socket colors, and an alchemy orb would turn a white item in to a rare item. There is even an orb called the mirror of kalandra that can duplicate an item, with the caveat that you can not duplicate a duplicate, or a unique. There are barely any items worth doing this though considering the rarity of a mirror of kalandra. Becuase there is no gold in this game, orbs are used as currency, for example someone might trade 3 chaos orbs for a piece of gear they want, or another currency. Trading is an important part of the game, however external websites make it easy enough to find trades, and there are self found viable builds.

Pros:
very fun to play, classic ARPG action with quite a few clever new adjustments to the existing formula
Dark atmosphere
clever game mechanics
Almost infinite number of builds possible
Fair business model, not even sort of pay to win
Provides a significant challenge at higher difficulties
Hardcore servers availiable, where death removes you from the league
new leagues come out all the time, which are sort of like servers with different rules
frequent PvP/racing events.

Cons
Economy on standard can get a bit ridiculous
Frequently complained about drop rates
without a carefully planned build, you can possibly be killed before you have time to react.

Tips for new players
Find a build off the official non steam forum that says beginners somewhere in the title
Don't play hardcore till you have gotten used to the game, and make sure to use a harcore viable build.
keep your elemental resists capped.
Make use of your flasks.