It's quite simply, the best fishing game ever made, and the only true fishing simulator on the market. I've played them all, fishing planet, the fisher online, call of the wild: the angler etc.
In comparison with Russian fishing 4, they are all mindlessly 'arcadey' mobile games with no sense of reward or accomplishment. Rf4 requires you to learn and think like a real angler, and when you do finally catch a fine specimen, you will feel like you really earned it. Unlike the other games I mentioned, fights in rf4 are intense, edge-of-your-seat battles that really take concentration and tactics. The standout features of the game include the best-in-class physics based fishing, where you can really feel the weight and strength of the fish as you fight them, where you simply can't in other games. Additionally, the game has an excellent team of artists (or maybe just the one who knows) behind it, and literally every item in the game from the hundreds of flavours of boilies, to the food crafting utensils, to every fishing hook is beautifully modelled and textured, you can see the love that goes into their work. The third and final standout feature I'd mention is the sheer amount of content - it's absolutely massive, and they are still adding more. There are so many different species of fish, all which have their own challenge and appeal, and every item of fishing gear actually feels significant, and handles slightly differently. Where the tackle in other games is immediately forgettable, you will learn the personality of every rod and reel that you buy in this game, and develop an intuition for what is good in different situations. Games that have this level of success in terms of how 'tactile' they feel, are few and far between. Only Mount and Blade Warband, and Star Citizen come to mind when I think of other PC games that immerse you in the game world through how physical the play feels.
I have to address the elephant in the room, which is the fact that it's a free to play game, and as with all free to play games, the business model negatively affects the gameplay, and in game economy, which in turn harms the player experience. The devs get unreasonably angry when you mention this simple fact in a review, and have treated players overly harshly in the past for criticism of the game. Those two issues are the basis for most negative reviews. Whether you will like this game or not mostly comes down to whether or not the positives outweigh those two negatives. Fortunately however, the devs have clocked on to the fact that they can't do PR or manage a community even if their lives depended on it, and have finally created an English-speaking branch of their company in the USA, and the result is that attitudes towards players have improved a great deal. Where comments on the steam forum would have been quickly deleted in the past, faster than you can say 'off to gulag', the new people patiently respond and treat players with respect. Because of those changes, the only real downside is the inherently frustrating grind that comes with free-to-play psychological maniupulation. If you want a seriously long-term game, as in one that basically never ends, maybe that won't be so much of a downside. When I consider everything in balance, plus the overall healthy direction the game is taking, the regular updates, and the soon to be added sea fishing expansion, I can gladly give this game 5 stars.
It really is the best fishing game ever made, by an extremely wide margin.