Recent reviews by Necroforge

Pros:
-the game itself is quite fun, taking aspects of Hearthstone and Magic and combining them in an engaging way
-fairly generous for a F2P game
-a good amount of game modes
-fantastic art and solid graphics
-you don't feel overtly forced to have to pay to win
-friendly and helpful community

Cons:
-Gauntlet mode
-unless you really truly enjoy competitive play or netdecking, then Eternal may not be for you
-Gauntlet mode
-the single player modes (Gauntlet in particular) are exercises in frustration, as the highest levels involve the A.I. basically drawing and playing god-hands, topdecking exactly what it needs when it needs it, and affecting your deck with mana screws or mana floods way too often for it to be random
-seriously, Gauntlet mode
-excessive grinding in single player

Personal Biases: I am a kitchen table CCG player, with zero desire to be competitive. Eternal, while a very well put together amalgamation of existing CCGs, relies too heavily on being competitive to be enjoyable to me. I would find myself playing games against the A.I. purely out of spite instead of for fun, as the A.I. is tuned to "soul crushing" at the highest levels.

tl;dr - A good competitive game, but if you prefer casual play then take a hard pass on Eternal.

EDIT: after an additional few weeks grinding through single player Gauntlet, my opinion is now a final and unequivocal AVOID IF YOU ARE PRIMARILY INTERESTED IN CASUAL PLAY (if you enjoy competitive play though, it is still worth a look). You will find nothing but utter frustration at the highest A.I. levels - much like the final boss of a fighting game - and any win on that high a level feels like all luck and no skill. Gauntlet (especially) is one of the most egregiously programmed single player modes I've ever come across in ANY game, whereas the A.I. is not overtly cheating, but it definitely messes with either yours or its own draws to gain every advantage, forcing you to netdeck if you want to have any chance AT ALL of winning any games (and even then, GOOD LUCK). There is no actual FUN to be had playing against the A.I. in any single player mode.