Of the people that I've seen who said that they dislike the games, it gets broken down as follows:
-Game's needlessly convoluted controls
-Intimidating lore
-Slightly middling voice acting
-Objectification of women
-An over-emphasis on maturity that leads to immaturity
So, to counter them:
-Put some time into learning the game and it's not that difficult: start with two crafted items, namely Samum to dispatch enemy groups quickly, and Swallow to keep yourself in the fight. The reason why you can prepare for fights pre-emptively is because the town merchants only ever sell books on creatures that you will encounter in the immediate area. The books aren't just flavour text either: they give you actual hints on how to kill the specified creature, and how to complete the local monster-hunting quest. Admittedly, it takes some getting used to, but it is worth putting the time in. Otherwise you only have yourself to blame for not paying attention to the tutorial or playing the Arena mode.
-All new lore is intimidating, but there are only a few things you really need to know between the games. It also helps that Geralt doesn't care about politics, so you're rarely under pressure when it comes to knowing the lore(besides, most of it gets explained in dialogue). Again, it's advisable to put some time in, but you don't have too much incentive to do so. It's essentially Tolkien-esque, except with a peppering of Eastern European political scepticism, and a way more faithful re-creation of medieval-feudalism society.
-Fair enough, though I feel the dialogue makes up for it.
-There are literally no 'forced' sex scenes. They are all optional in this game, and the ones including Geralt's love interest, Triss, are tasteful without being too 'srs bznz guiz' or cringe-worthy like other games *cough* Bioware *cough*. All the non-optional ones are consensual ones used to blow off some steam for both parties, like you know, actual sex.
-This depends, though it's often lead in with the previous point. What people usually mean in reference to maturity to these games is the grey area in everything. Nearly all quests are intricately designed so that if there is a choice, it's never as clear-cut as it seems: you go in with the expectation that the best choice is always the more difficult one, again, just like in real life. The reason why it's mature in terms of the story, is that there are no good guys except for Geralt. It's a shitty world where having power inevitably leads to arm-twisting of varying degrees, and those with power abuse it constantly. Even when it looks like a leader with genuine and good intentions might change the world, it's ultimately fruitless as they will be exploited by a greater power. It's mature because the game relies on your own moral compass to guide events, just like how Geralt does things, and ultimately, you are only ever concerned with keeping those you care about safe.