They are all grindy as fuck by design. The monetization model is to make it grindy enough to get people to spend money on shit. The vast majority of them have rather boring gameplay. Typical incremental or collector game systems. The overwhelming majority are unfappable. They have nice art, but is usually vanilla, have flimsy overarching stories, and don't typically have full fledged scenes.
I've played around with a few, but there are 2 games that I personally played for a long while. Cunt Wars has decent gameplay. You can take it easy and slowly improve your deck. I had fun with it for a long while and am just starting to get bored of the grind. I still log in to direct the Turf War for my guild, but kinda stopped doing the daily grinds. 0 fap worthy content, but there are some great eye candy CGs.
Taimanin Battle Arena is pretty much the only fappable Nutaku game in my opinion. If you like typical scenes from Lilith games, there is a gold mine here. It takes a bit of dedication to get into the top50 to get the important event rewards as a F2P player, but you absolutely can, at least when I was playing it a year or so ago. It felt pretty fun as well once you get into top50 and cal snowball without spending.
I'm sure others have their own guilty pleasure from nutaku, but you just need to accept the fact that these games are designed to strike that balance between player retention and player spending. Make it too P2W and you lose the player base. Make it too F2P friendly and they are losing out on $$$. And and all these games will shower you with resources when you first start then taper off once you are hooked. Some miss the balance and make it extremely frustrating if you don't spend. Some make it more fair and give you a decent sense of progression for F2P.