Sins of a Dark Age is a MOBA that's not as hardcore as say Dota 2 or HoN but at the same time not as casual as LoL, HoTS or Strife. It's somewhere in the middle and I like that.
In this game you can't deny creeps nor towers and you don't lose the gold when you die. The game has a gold sharing mechanic; If you kill the creep you will get the full amount of gold from the kill while your teammate (if he was nearby) will get half the amount of what you got.
The game also has a Glyph system. Think of them as something like 'Summoner Spells' but you don't pick them before the match but rather once the match starts. Which is a great thing, because you can pick glyphs based on which enemies you're against. You can also upgrade them in match once you reach certain levels. Each glyph can be upgraded twice, each time choosing between two different upgrade choices.
Then there's also Quest System. The quests start at certain points in the game and are randomly picked for each match from a pool of quests. Each time you manage to win a quest your team gets a permanent bonus for the entire match. There are 4 tiers of bonuses.
While quests are worth doing, they're not a must. You'll have to decide do you want to do the quest or will you rather stay in lane and farm or push and destroy enemy towers. The enemy team has to make the same choice. This is where things get interesting and really make each match different because what you're going to do depends on the current situation in the match.
Another interesting thing is the crafting system. After each match you'll get a reward and it'll be either crafting recipe, materials, lore pages and if you're lucky you could get a skin.
You can craft hero skins as well as gear items (you can equip your heroes with them before matches to gain small bonuses). It's fun and it basically allows you to get all skins and gear without paying anything (you can buy skins in the game's shop if you don't feel like bothering with crafting, gear on the other hand isn't available in the game's shop). You can trade items with other players and you can also buy or sell them on steam market.
The game currently has 5v5 and 2v2 modes. There's also 5vsAI. Developers have said they plan to add more modes in the future too.
There are only 20 heroes in the game at the moment which is not surprising considering the game is new. However each hero is fun to play with and feels different and there is a fair amount of heroes of each type (carry, spellcaster, tank, support, assassin). Developers will of course continue adding more heroes over time.
To wrap this review up I'll say the game is really great, a lot of fun and I would definitely recommend it. The only problem some people have (including me) are optimization issues and stuttering but that's something the developers are working hard to fix and hopefully wont be a problem anymore in the near future.