What crossover games need is a special feeling. The prequel to this game somewhat managed to capture that, but some fine tuning could have gone a long way. Capcom vs SNK 2 managed to do that fine tuning.
The stages mostly feel special, but I will admit there are only a few of them here. I could have used more stages, personally. Get rid of the one with the windmills and New York, those are lame. The roster got some additions to make this feel a bit more like Capcom vs SNK instead of Street Fighter vs King of Fighters.
More importantly, the Groove system added some depth and it's mostly appreciated, barring a few grooves that can be unbalanced (A, K). On top of that, you can actually choose how to spread the Ratio among your characters. Major game changer right there. There's also a 3-on-3 mode if you don't want to bother with the Ratio system.
With the large cast of characters, the teams you can make, the way you can make the same teams play...there's just so much replayability right there. Plus, you can get different boss battles depending on the Groove Points you get during your playthroughs. Due to this, you can get better endings to this game than in the prequel, where you basically had two that looked poor.
There are also unlockable modes and you can get Shin Akuma as well as God Ultimate Rugal.
On top of that, the soundtrack is a vast improvement over the previous game, if you ask me. "This is true love we're making" pretty much kills the CvS soundtrack by itself, sorry, I don't make the rules.
The PS2 port holds up its end of the deal well enough, we're not talking about some weak PS1 port here. Playing this with a Dualshock 2 controller is a great experience.
Graphically, the 2D sprites are top notch. As I said, I'm not really behind mixing that with 3D stages, but most of them look good enough. The music's good or even great, and there's enough reasons to keep playing. Okay, maybe they could have taken the Marvel Vs. Capcom 2 approach of having more characters to unlock, but that just depends on how you look at it. I like having almost everyone available from the beginning, so there you go.
Now, consider this the end of the regular portion of the review. Stop reading if you don't want to get too deep into the mechanics of the game.
After digging into the competitive scene, I found that this game does suffer from some balance issues. For instance, one of the biggest features that will favor a character is how good their simple, normal attacks are. The mere "buttons" of a character, if you will. Blanka has some great buttons, as does Sagat, and thus, they are very highly recommended to use, even if you're a casual player. I mean, you could also just use the busted boss characters like Shin Akuma, God Rugal, Evil Ryu and Orochi Iori, but if you want to keep things fair...Blanka and Sagat.
This leads to a question: which groove is the best? The answer for every character is the K-Groove, it simply has too much of an advantage over the rest with its Rage mode (when the character glows red, and indicating that their attacks are considerably buffed). The ability to enter Rage mode by taking damage or executing Just Defends (i.e. blocking at the last second) provides a massive damage boost and access to powerful level 3 supers at a relatively low cost. This mechanic allows for aggressive play with high payoff, and on top of that, it's not hard to fill up the K-Groove meter. You could make an argument for the A-Groove, though, that's based on the V-ism from Street Fighter Alpha 3. This means that if you enjoy going into the training mode to test Custom Combos with this groove, use it. If not, go for K-Groove.
The worst Grooves are P-Groove and S-Groove. P-Groove is inspired by Street Fighter III's system, which has Parrying, hence the name. What's the issue with it? It takes an excessively long time to build your meter here, limiting access to super moves, which are crucial for dealing significant damage or turning the tide of a match. Plus, with the weakest guard bar and no guard cancel or red parry, players are extremely vulnerable to pressure if they can't parry effectively. If you're reading this and don't even know what parrying is, do not, ever, use this groove.
It may surprise some to see the S-Groove here. It's based on the early KOF games, where having a low amount of health left means you can use infinite level 1 super moves, at no cost. Sounds great, what's the problem? Well, level 1 super moves have poor priority, meaning that the opponent can hit you before you manage to execute the move. This means that you'd only really make use of these in situations where you can spam supers, which is a gimmick (i.e. if your opponent knows what's happening and how to counter, it's useless). You can charge your meter, but at high levels, even the AI isn't going to be nice enough to let you do that.
I won't get into tier listing. However, if you want to know what characters to avoid using, since this is a big roster: Dan (literally a joke character, parodying Art of Fighting), Kyosuke (I wonder why they even put this guy in the game), Dhalsim (he has the most unfortunate hitboxes in the game, imo), Yun (why is he alone? I know his brother makes a cameo in a super move, but it's one of the worst supers in the game).