Oh boy, this is a subject close to home for me. So Maplestory sits at my favorite game of all time, it's grindy, buggy, childish but even today I find it stupidly fun (despite me not playing regularly). It was F2P since it released and for years it was pretty good, the cash shop was pretty much just for cosmetic items, and pets that would auto use potions at certain HP/MP and pick up items for you. It wasn't fairly priced but it barely affected gameplay (at least from what I remember).
This all changed when the fire nation attacked Nexon (the publisher) decided to implement a system like Diablo games (from what I know) where gear has bonus affects that you can identify by paying with in game currency. They tiered this in such a way where better items with better "potentials" (the identified stats) were given a ranking, and this is where the F2P model when from fair to the most disgustingly P2W shit ever. Essentially you could drop a few dollars in the cash shop to reset the potential, and have it be better or worse when you re-identified it (with some limited time cash items guaranteeing a potential increase). This lead to hardcore players dropping THOUSANDS of dollars to get the best gear, but essentially gambling their money away.
So yeah, to answer your question I hate F2P models and I think they're ruining games. I love MMOs and they're worst hit by it, any F2P MMO makes me feel like a second class citizen when I don't pay, so I only play P2P ones now. Sure you can argue "But they're businesses and they're there to make money" but in almost all cases I've found F2P turns into showing no respect to players even if they do pay. This is why im so worried about the DFO relaunch.
Although it must be doing good by raking in fuck loads of money if this many companies get away with abuse.
Once it goes past cosmetic in my opinion it becomes bad.