Want another unique feature? In what is likely an effort to derail gold farmers, Path of Exile doesn't include any sort of in-game money. Instead, whenever you sell items, you receive back fragments of scrolls or shards of orbs. Currently, you can only receive one type of scroll this way -- Scrolls of Wisdom, which are used to identify objects -- but there are a variety of orb shards, including one set that combines into Orbs of Alchemy, which convert "normal" items into "rare" items. The payouts from the vendors are reminiscent of the Horadric Cube recipes from Diablo II, which means you have to pay attention (and perhaps use the generous equipment stash found in each town) to maximize what you get back from the equipment that you sell.
Other parts of the game aren't as unique. For example, the world is divided into acts, and each act features a hub town where you can do some shopping and pick up some minimalist quests (usually to go out and kill somebody). In between the towns there are distinct map areas, where the theme and level of each area is fixed, but the layout and the enemies are random. After every two or so map areas, you find a waypoint, which allows you to return to town. If you don't want to wait for a waypoint, then you can also use a Portal Scroll to return to town. Then when you finish exploring the map areas for one difficulty setting, you can repeat the process at a higher difficulty setting. If that doesn't sound familiar, it should. It's taken verbatim right out of Diablo II.
Or consider the equipment, which comes in four flavors: "normal" (basic items), "magic" (1-2 extra bonuses), "rare" (4-5 extra bonuses), and "unique." Item drops are always random, and the bonuses are for things like your damage, your attributes, and your chance to find better items. There aren't any set items, at least not yet. This is roughly the same system as used in every action role-playing game, and it works about as well here as it does elsewhere. The most interesting thing about the equipment is how Grinding Gear Games handles potions. Instead of collecting stacks of potions or gathering health and mana balls as you fight, Path of Exile uses flasks. Flasks can contain health or mana or both, and they fill up as you fight enemies. That means you don't need to constantly replace your flasks; they're a part of your equipment, and you use them over and over again (and they can be "magic" or "rare" just like other items).
Finally, in its current state Path of Exile only has an online mode, where an Internet connection is required to be able to play. But you don't have to group with other players. The more people you have in your party, the tougher the enemies are and the better the loot is, but equipment just falls to the ground, where the quickest player can grab it, and so grouping is something of an iffy proposition. But nicely the towns in the game are world zones where players get to mingle together (as opposed to the combat areas which are instanced for each party), and so the towns help to make Path of Exile feel more like an MMO rather than a collection of instances. Path of Exile also includes various leagues, where different leagues have different rule sets (including a hardcore league where you can only die once). The default league is friendly and cooperative, but in other leagues you might be allowed to attack and kill other players, or you might be rewarded for reaching a certain goal first.
When I first heard about Path of Exile, I thought it looked like a lightweight Diablo II clone. But after playing it for a while, I'm prepared to at least drop the "lightweight" part. Grinding Gear Games was clearly influenced by Diablo II, but they've added enough new features -- and, whoa, enough complexity -- for their game to stand apart. Path of Exile is also currently a 2GB download even with its campaign only half finished, and so there shouldn't be any confusion between it and those free-to-play browser games, either. It's tough to say how successful Path of Exile might be -- especially with Diablo III just around the corner -- but so far it looks like it's on the right track, and you certainly can't beat the price.