Fel Reaver is great against other aggro deck, they don't have any answer for it. Face Hunter can't deal with it.
it's a coin flip against control, specially control warrior (well it's the only control deck anyway lol), you can't hope to hit face with it really, you should probably don't play it unless you think they don't have the answer.
it's really a bad idea to play it against any mid range deck, they can punish you really badly.
It's suicide to play it against combo decks, well basically rogue now, rogue can win the game right there...you gotta be yolo to play it there, it's never a good idea. I recall earlier this season playing patron, these aggro druid just hit fatigue in like turn 6. It was hilarious. Cruel Taskmaster, inner rage on CT, Battle Rage, Execute. lol that's 12 cards right there. Good times.