TL;DR If the game is <$15 buy it IF and ONLY IF you like Arkham-style gameplay and don't care about Lord of the Rings Lore being trampled and also don't care about Denuvo (buy on GOG for Denuvo-free).

Would never have bought this at launch: it had horrific microtransactions, lootboxes, and progress toward getting the ending was locked behind rare drops that could also conveniently be purchased through the lootboxes. All of this was removed a couple years after release, and I played this after I got it through the Humble Bundle. I'll review it at it's current state, in case all of that didn't turn you off.

Big CON: still has Denuvo DRM.
Cons:
1) Endgame is a tiny bit grindy and relatively light on story. It feels more like NG+ than an actual ending arc, but it doesn't leave any loose ends, really. You may therefore either view the ending as relatively satisfying or relatively hollow. It depends on how much you connected with the main character(s).
2) Story is completely Non-Canon. If you were looking for a story that fits neatly into Tolkien's established lore, look elsewhere. The story is complete fanfiction, but it isn't absolutely atrocious, so it's decent fanfiction. It does take massive liberties with the lore (especially regarding Sauron, Shelob, and Celebrimbor), but if you're willing to view the story as an alternate universe, then it isn't that bad.
3) Online play, while it can at times be fun and interesting, is overall pretty gimicky, consists of almost exactly the same gameplay mechanics as offline play, and you basically need to have completed the single-player game first to be able to effectively complete online assaults. By that time, especially with the somewhat-grindy endgame that you've gone through, you will likely have had enough of the gameplay that this game has to offer.

PROS:
1) Fun Arkham-style gameplay. This is why you would play this game. The movement and combat system are smooth, polished, and enjoyable. Mistakes are punished appropriately. Gimmicks keep you on your toes and provide variety and sometimes necessitate a change of tactics.
2) Army building/Collection. Unlocked after early-game, this mechanic scratches the universal itch all human beings have to collect resources. Maybe this is why HR departments become power-tripping tyrants...
3) Good visuals, good voice acting, decent music, orcs have amusing voicelines and captains can have interesting personalities that encourage you to add your own interpretation to them.
4) Doesn't outstay it's welcome. Although the endgame gets a bit grindy, I found it to be just about right for the amount of time I would want to play this game. Beat it once on Hard (or easier diff if you're a casual, no shame), try some online assaults if you aren't burned out, then stop playing and be satisfied with your experience (as long as you didn't spend too much to buy the game, like the $50 price tag).

I have played 19 hours in one day. Take from that what you will

Nobody will read my review so I Will Eat 1 Tablespoon of ketchup For Every Like this gets.