I own 662 and 662F. They both sound A LOT better than their ridiculous price [$35] would suggest.
However, Imo 662F is clearly the better headphone.
Regular 662 are seriously V-shaped. They have a lot a "punch", with heavy lows and aggressive highs.
Add to that the great seal they offer and there you have a good studio tracking headphone (perfect for a drummer) or even a DJ headphone (the cups cannot rotate but the band is very flexible though).
But their colored signature is fatiguing. Plus the mids are recessed and mediocre, they lack refinement and the pronounced top end sounds artificial/annoying.
The 662F is a neutral, highly detailed and unforgiving headphone for monitoring purposes.
Precise treble. Mids in check, neither prominent nor recessed, nice.
Bass is clean, digs pretty low, is impactful and has an amazing texture.
Seal is excellent.
For a fully closed headphone the 662F offers a superb soundstage, with great separation and imaging.
Analytical, highly detailed and neutral sound. Not for everyone but great mixing tool though.
For... $35 (35!) you will get something almost as good as the Shure 940. A kind of closed little brother of the Q701 or something.
If you like acoustic music, jazz, folk, strings,.. chances are good you will love those.
(Btw, the Superlux 681 EVO - also $35 - may be a great alternative if you are looking for a warmer signature.)