If we were to compare this game directly to CS1.6 and CS:GO right before CS:2, I would have to say this is easily the worst counter-strike game in the series.
Textures are clear and crisp, and lighting effects have aged quite well, but maps are hilariously poorly lit and way too dark, the torch has visual bugs on a few maps and makes it harder to see than easier (double doors on aztec). The game runs excellently and has visually aged quite well, but low polygon count is highly noticeable, and I find the game is quite ugly to look at. It also went for a very cartoonish artstyle for character and weapon models, which clashes with the otherwise photorealistic style, likely photo-sourced textures.
I only play with bots so I can't comment on multiplayer performance, but even when hosting your own server to play with bots, the extremely poor netcode is immediately and readily apparently. Characters have a delay before ragdolling after dying, shots can seemingly miss despite being clearly on target, and bots can fire at you behind walls and land non-wallbang kills.
Regarding bots, their skill level varies considerably compared to 1.6. Whereas in 1.6/CZ, bots of a certain difficulty level would vary in skill level (you can tell by their name), that variance was small enough that most games would be fairly matched. In the case of Source, bots appear to vary in skill level considerably in a single skill bracket (I've only tested against Hard bots, unsure about other difficulties) and also vary in performance round-to-round.
Bots have some improvements over 1.6 bots, including generally better pathfinding and decision making skills, as well as improved weapon control, but those are the extent of the positives. They frequently jump in place randomly, especially when turning corners, they occasionally throw their weapons away for no apparent reason (No weapons on the ground to pick up and replace), they sometimes shoot the ceiling for no reason, and they always shoot destroyable objects if they path into them, even if they can path around it. They also tap fire SMGs and have improved running accuracy, apparently.
In terms of weapons, accuracy in general is significantly improved over 1.6 - Mainly, the AWP can actually be used, and long distance AK taps are possible now, which are simply not possible in 1.6. However, the spray patterns CS:GO players will be familiar with don't exist, so consistent and reliable full-mag spray prediction is impossible for most weapons. This is generally and improvement, although TTK is a bit too low for my tastes and the game can play a bit quickly with bots rushing in and standing still to die to a firing squad.
Economy is simply broken. While it should be well known that 1.6's economy is poorly balanced, CS:S's appears to be even worse. T's can consistently buy AKs second round regardless of whether they won or loss, which is an utterly mind baffling balance decision. Since the only economic setting you can tweak is starting money, there is no feasible way to adjust this in game to fix it. Overall, due to economy alone, the game is rather T-sided in almost all cases, except for exceptionally poorly balanced maps.
Almost all maps are source ports from 1.6, and follow a similar layout. Havana changes per round which is an interesting trick and can be fun to experience. Overall, they are their poorly balanced, early counter-strike selves.
In general, I consider this game to be quite poor, although there are a large number of features to like about it. So, why the positive review? Well, it's not 2004 right now, and CS:S is not a game you buy and play for the gameplay of CS:S:
1. This game comes with the orange box, so you either already have it for free or can get it for cheap alongside other, more interesting games
2. The game's assets are required for some gmod maps, and although I don't play gmod, that alone is a good reason to buy it
3. It is still playable over 2 decades later on extremely low-end hardware due to impressive optimisation and bot support, and although the bots kind of suck to play with, they're better than nothing
With those considerations, it would be a bit pedantic and silly to give it a negative review just because the core game is of poor gameplay quality, given it's already marked as the black sheep of the counter-strike family and serves a different functional purpose as a game you purchase in the modern era.
