Swashbuckler is a great class... for three levels. After that, you can smell a "real roleplayer" or someone new to the game by the number of levels they take above three.
Seriously, though, it fills a niche, but doesn't do a terribly good job of it.
Hexblade is basically an arcane, debuffing version of the paladin. Since debuffs are weaker than buffs and arcane spells generally weaker than divine, and the paladin gets more side goodies... yeah. Once again, interesting and flavorful, but weak.
Knight won't necessarily live up to the idea the name of the class conjures, but is a very good class. It's only downside? One of its main mechanics is CR-based (ugh). Nonetheless, it's worth inclusion in virtually any campaign.
Complete Warrior is a fairly average entry in the Complete series. It has two of the most famous offenders for "brokenness," the Frenzied Berserker and the Hulking Hurler, but in truth both are overhyped. The Frenzied Berserker is an anti-party character; essentially, it's not for PCs. To become broken or even powerful, Hulking Hurler requires Large size, a PrC from the Miniatures Handbook, and one poorly worded rule in the back of Complete Warrior. The rest of Complete Warrior trends toward the weaker side of things, particularly in the three base classes.
My opinion of this book has dropped over the years. in particular, the PHB2's high-level fighter feats and the Book of Nine Swords' alternate warrior classes have made many of the once-nearly-required-for-fighters PrCs and/or feat combos in CW irrelevant.
The PHB2 is almost certainly a better buy than CW at this point, although IIRC it carries a higher MSRP. The difference between these two books says a lot about how much more WotC's designers 'get' 3.5 than they did when CW came out. Fighters go from back bench to borderline all-star with the additions in PHB2, while the other core classes get options that are interesting and balanced without actually upping their power.
Dread Necromancer can be broken wide open by combining it with a feat, IIRC, giving you unlimited free self-healing. Which might actually be a plus for an NPC
. Or, heck, for a PC if you want to escape per-day balancing. Anyway, it's otherwise a nice enough class and won't cause any other problems.
Warlock is a bit weak if you follow the reccomended average encounters per day, very weak if you average 1-2 encounters, and strong if you average more than 4. It's a well designed class across the board, although a bit tied to its flavor considering how universal its mechanics are. As an NPC it will usually be a) easy to run and b) weak, the latter because most NPCs show up for only 1-2 encounters in a given day.
