Best in series, but definitely not without it's flaws.
When the first Soul Calibur debuted in arcades it blew everyone's minds. It has most definitely aged gracefully (I'm STILL blown away at how good the game looked compared to all other games on the scene at the time), and the game play is so refined and balanced that it can still be gone back to and played today without a hitch, even after having gotten used to the latest incarnation. That's a whole lot more to say about Soul Calibur to which most other first-in-series games can even come close. The second game basically took everything the first did correctly, fixed anything that went badly (I can't think of anything, really) and applied it to more characters, much more detailed and vibrant visuals, and on a much grander scale with 3 multi-platform releases, introducing the concept of console-exclusive guest characters in the form of Spawn, Link and Namco's own Heihachi Mishima, which made for the best Soul Calibur yet. The third game in the series went back to console exclusivity on the PS2, which hampered sales (especially after the critical success of the previous game), and made some slight changes to the mechanics of the game. III mostly wasn't received well by fans for many reasons, including an almost gamebreaking bug in the most important mode, and since it didn't have a major release in arcades it wasn't taken to the same competitive level that the first two were; especially since it still lacked online play, but you can't blame Namco, given the horrible state of online for fighting games, especially on the PS2. But, having introduced 3 of the coolest characters in the entire series, more game play modes than ever before, better graphics than what I still think are possible on the PS2 and (finally) a character creation system that was well beyond anything gamers have ever seen in a fighting game, the SoulCalibur III was, up to that point, the best in the series in my humble opinion, even with it's flaws.
Well, now the long anticipated SoulCalibur IV has been released, losing the PlayStation-brand exclusivity that undoubtedly plagued the first game's sales, raising the bar for graphical achievement in fighting games, game play that hearkened back to the good ol' days of SCII, re-implementing console-exclusive characters and giving fans what they've wanted since the first, ONLINE PLAY!
Soul Calibur IV does have it's bad things along with it's good, like all other games, but some of the good things are also unusually the bad things (i.e. the StarWars guest characters). To get this out of the way, Yoda sucks! He's too short to hit most of the time, you can't grab him (he can't even grab himself) and his moves are way too over the top for the sake of being way over the top. The Apprentice is a cheap b**ch! He's a bastard from the planet Basterdai because his moves have unbelievable range even though he's one of the smallest characters in the game and his Light Saber is about as long as Mitsurugi's Kitana or Raphael's Rapier and they take off more HP than they should and his Force Lightning moves are about as stupidly out of place in a Soul Calibur game as he and Yoda are theirselves! Even when you play as him you hate him because his moves are so overpowered that you can't help but think of the match as unfair. I hate him and he should stay in his own f***ing game! As for Darth Vader, he's the only well rounded character. His moves aren't too easy to pull off and even when you get the hang of playing with him, you never feel like you won cheaply because they take a relative amount of skill to pull off, as opposed to the other two. Even though I really liked Darth Vader in this game, I still think they shouldn't have included any StarWars characters. We would definitely have benefited from Namco introducing another new Soul-series character that plays similarly to Darth Vader (minus some force powers) and put him on both consoles instead.
The character creation system in Soul Calibur IV is also another double-edged sword. The mode is definitely bigger, more detailed and more seemingly endless than any other create a character mode in most any other game currently out on the market. The amount of items you unlock and purchase seems to be endless and you can now alter the muscularity and physique of your character. You can't alter seperate body parts, but at least it's a better, more detailed option than in MK: Armageddon, where you just chose small, medium and large body types. Now you can even alter the entire outfits (including hairstyle) of existing SoulCalibur characters, save for the guests and the boss and they've also included 50 (FIFTY) slots for custom characters! Yes, that's 50 (FIFTY) possible characters you can create! So why is this also a bad thing? I mean, it sounds perfect! Right?... It would be perfect if it weren't for the execution of one certain aspect. Every single piece of armor and clothing you equip for your character gives a certain category a certain amount of points. The categories are Power, Impact, Guage, Boost and Sepecial and the higher the points are under each category, the better the skills you can equip, such as regenerating your health bar with every hit to your opponent, automatically escaping any throws or completly nullifying any ring-out attempts by your foes. If you don't have enough points under certain categories then you can't equip certain skills, and if you really want those specific skills you need to change your characters appearance (sometimes even including the weapon which they wield) in order to gain enough points to equip the skills you want. You unlock skills by leveling up your character (9 is the peak...which is ridiculously easy to achieve), oh, and the appearance of your character also alters the ammount of health they have on a scale of 200% (100% being one full life bar, and 200% being a second full, blue bar). So you can basically go into the mode and make the exact character you want and then realise they have 65% health and you can't equip more than one or two low tier skills that are pretty much ineffective. This isn't a problem if you play standard versus online or off, but you'll be screwed in special vs., and the single player Story and Tower of Lost Souls modes.
Story mode is basically pointless except to gain Gold as their are only 5 stages and the endings for every character (without exceptions) are pretty stupid and Arcade is just a way to gain Gold and level up your character (which will take no more than one or two playthroughs, max, for the same character. Tower of Lost Souls is awesome, however. You chose to ascend the Tower of Lost Souls from floor 1 to floor 60 unlocking treasure chests that give you items for character creation and you gain plenty of Gold along the way. Every match has certain stipulations and requirements you must follow and meet in order to progress, i.e. defeat all opponents before time runs out, and before certain matches you are also given a clue as to how to unlock that floors treasure chest, i.e. "You are not alone", which means you must change with a partner at least 2 times before the match ends. Those specific stipulations don't affect progress, though, only whether or not you unlock the treasure. That reminds me, Namco has implimented a tag feature that is more seemless than in Tekken Tag and even better than Capcom's vs. games with some floors allowing you to chose two character and some allowing you to have three! Too bad it's limited to this mode. After a certain amount of floors have been ascended, you can chose to descend the tower in a survival mode of sorts until you reach the bottom floor. You are literally given no breaks between floors and there is no way to regenerate health unless you have a skill equipped that regenerates your health, which makes the way you customize characters very important. The thing is, it's hard to tell whether this mode is awsome because it really is awesome or because most of the other modes suck so badly, and it's extremely and increasingly frustrating along the higher floors to the point where you'll probably just stop after floor 40-something.
There is one implimentation to the game play that has garnared quite a bit of controversy; Critical Finish. Much like the MK series' fatality system, a Critial Finish move is a......finish move.......that, well, finishes the round. Once it is excecuted.....the round ends. There really isn't anything left to say except that most of them are awesome! So, you have this guard meter, much like in latter Street Fighter games, and the more you guard the more it depletes. During the depletion of the meter your character's armor and clothing get damaged and when a certain piece of armor or clothing get's broken or torn they recieve more damage when hit on that area, and they stay like that for the remainder of the match. You can even still see the broken armor and clothing pieces on the stage. When when the Soul Guage, as it's called, depletes all the way, the next blow that is guarded causes the blocker to go into a guard crush and before they recover their adversary can push all four face buttons at once to unleash an elaborate, pre-rendered Critical Finish move. It was implimented to prevent players from turtling, but it takes soooo long to deplete the guage all the way that I've never done more than one Critical Finish in a match and I've been playing the game almost every day since release. So don't sweat it, ring outs are still the fastest and cheapest way to win matches.
Online play has been introduced to the series, and to say the least, it's fun and relitively lagless. You can chose standard or special vs. modes like in offline matches, and even chose to have your wins and loses tracked or not in either ranked matches or just regular player matches. It's fun and is the difinitive reason to own SoulCalibur IV if for nothing else.
All in all, much like SCIII, Soul Calibur IV is the best in the series despite it's flaws because the gameplay is true to itself, the graphics are astoundingly gorgeous and online play is executed pretty successfully. The game is impressive, but only where it's ALWAYS been impressive. SoulCalibur IV is successful competetively but it doesn't excel with it's single player aspects. If you are a fan of the series, it's obviously a must have, but for everyone else, it's only worth a rent if you don't plan on playing online or with friends.