The 'Souls games are their own very unique thing, so while some love them others will bounce straight off. I played a chunk of Dark Souls and decided it wasn't my thing but it still deepened my respect for the series. There isn't really anything you can compare them to outside of the series.
The core of it is an extremely dark, European medieval fantasy with deep Bible-scale lore and supernatural elements. It's most basic premise is you are a soul literally fighting your way out of a gothic hell where nothing is quite what is seems and the game play is designed to reflect that. It's a gruelling journey. Every enemy can kill you easily if you're not careful and death can be a significant setback, so the stakes of most encounters are high.
You can approach the challenge with a wide variety of character classes but you are not a nimble, indestructible fighter - you're a slow & clunky knight in armour, or a physically feeble wizard, or a lock-picking thief in a loincloth. Weapons degrade. Experience collected as "souls" from slain enemies can be lost when you die. Save points and opportunities to level up are sparse. Bosses are powerful, frequent, & radically different each time. You will die many times.
Like I said, it's not my thing. However if you want a genuine challenge with interesting lore, phenomenal art, and some brilliant monster design, I would definitely give one of them at least a go. I'd honestly recommend everyone at least try to play one at least once, even if you then walk away, just to see what it is.