VF is by far the deepest game. Looking at my av, you probably say that I’m bias, but at the same time, I’ve played and studied Marvel, Soul Calibur 4 and 5, and DOA among a few others, and I’ve also tried to learn Tekken to a certain extent.
Now ‘deep’ is kind of an ambiguous term. Deep, IMO, has to do with the number and level of strategies you can employ in your gameplay. Having a big list of combos that you can pull off doesnt really make a game ‘deep’ if it doesn’t take much brain power to get that first hit to begin with (like Vanilla Marvel Phoenix or 3s Chun). Now, as much as I dislike SF4, I love watching streams of it with high-lvl play; in comparison with other games, SF (sans 3) characters don’t have many offensive or defensive options to choose from, but what makes it exciting for me to watch is that high level players take even the smallest details of seemingly routine abilities, such as walking and jumping etc, that can be easily overlooked by lower-level players and casuals (walk speed, jump arcs, max range of each attack for footsies, manipulating hitbox ranges for unblockables, etc)
VF has all that, and way more options available at a given moment than any other fighting game. So when considering your strategies to beat your opponent, there are way more scenarios to consider at any given moment. And because of that, VF becomes less about solely exploiting your character’s given abilities to force a win out of them (the part I dislike about SF4 and Marvel), and more about manipulating your opponent into logical traps.
Now for example, take okizeme. You can blast me if I’m wrong (definitely no SF expert), but in SF4, when attempting oki, you have to consider whether the knocked-down opponent will quick-rise or not and whether or not they will reversal you (if they even have a reversal). In VF5FS, when attempting oki, the first thing to consider is whether or not your opponent will tech. And if they do tech, what direction will they tech (teching in place (i.e. quickrise) will force them to stand up, which is weak to throws, and side tech forces them to get up crouching, which can be blown up by launching mids)? If your opponent DOESNT tech, they now have access to back roll. They also have access to wake-up kicks, which are univeral oki reversals, and are also 50-50s (mid or low). They are -6(safe) on block, unless they risk doing a backroll wakeup kick for added space, which is -15 (>kick-class punishable). They are very viable reversals, but they also can be blown up in a variety of ways (some characters also have better options to specifically blow up wakeup kick than others). But then again, your opponent can also NOT tech and NOT use wake up kicks, so that’s another thing to think about.
From the above example in VF5FS, just from a knockdown you are now presented with nearly a dozen options to think about, and you have less than a second to respond (high lvl VF is as fast as Marvel btw). The ways that you can respond are even more numerous, and all have different levels of risks/rewards. In order to respond correctly, you have to deduce your opponent’s habits (dat VF yomi), and as fast as VF is, your observation skills have to be on point to be able to respond correctly on multiple occasions in one game. And to win, you have to manipulate your opponent by cutting off certain options of theirs into a predictable set that you can exploit (example: attacking aggressively on a defensive opponent to make them susceptible to a throw, which is what guard is weak to in VF.). The number and level of options available to a player at a given moment is largely determined by frame adv/disadv, which is why frames are so important in VF
As far as other 3d games, Soul Calibur and Tekken have very little in common with VF. Namco games are very defensive in nature IMO, the best players are the ones with the best blocking skills and movement - they are games based alot on footsies and poking. Also, throws are less effective, as in SC, they are nearly always 50-50s, and in Tekken they are seeable and you can break them (nearly?) everytime if you can react to the specific animation fast enough. This makes blocking really strong. Punishment is way more important in namco games, unlike VF, where the vast majority of moves are safe on block. I’d say the difference between SC and Tekken is that Tekken has a bigger emphasis on mixups and SC focuses more on spacing.
DOA is more like VF, but with alot less options to choose between and deal with. I hear people call it VF lite. DOA also has a stronger emphasis on mid/low/throw mixups and strings than VF