OA Samurai have strong Will saves as well as strong Fortitude saves, plus better skill points and class skills than a Fighter. And they get Ancestral Daisho, though it's not a great ability, but it's something at least. In exchange, they give up a few bonus feats and some of the Fighter's larger selection of bonus feats to choose from, and Samurai have to remain of Lawful alignment and follow their code. All in all slightly stronger than the Fighter, but only until you consider the feats available to Fighters in the 3.5 Player's Handbook, Complete Warrior, and Player's Handbook II. Then they're probably about on-par, give or take just a bit of overall power, though Fighters are definitely a tad better in damage-dealing due to Weapon Specialization et al. OA Samurai choose one of the Rokugani Clans to learn their bonus feats from (i.e. Crab Clan gives access to bonus feats for hitting hard and toughing it out, Dragon Clan gives access to bonus feats for two-weapon fighting and ki shouts IIRC, Scorpion Clan gives access to bonus feats for deceptive and clever fighting, etc.), but these can just be redefined as different dojos or martial arts styles in any other setting.
In Oriental Adventures, the Ancestral Daisho ability gives Samurai a free masterwork bastard sword (katana) and masterwork short sword (wakizashi), representing the Samurai's honor and duty respectively. It allows them to enhance these weapons through meditation and sacrifices to the spirits of their ancestors and the Fortunes/Kami/whatever, with certain values in GP for different degrees of enhancement. The minimum and maximum enhancement possible depends on their Samurai class level. The Samurai chooses what enhancement bonuses or equivalent special abilities to imbue their daisho with; so the Samurai can have a +1 honorable returning katana of throwing and a +3 defending wakizashi of ghost touch at the middle levels, for instance, without needing to find these particular items in a magic item shop, or without needing to find a friendly spellcaster who possesses the proper feats and spells to create these specific items.
The Rokugan book (which is also 3.0 like OA, not 3.5) adds some Minor Clan bonus feat lists for Samurai, as well as a variant to have Samurai pay some paltry XP for Ancestral Daisho enhancements instead of the much more significant GP expenditures noted in Oriental Adventures. Rokugan also adds several overpowered feats that Samurai can take to be equal or better Fighters than Fighters themselves. One of my major beefs with the Rokugan book's shoddy balancing. The Rokugan book also adds Void feats and allows a human to take the Void Use feat in place of an ancestor feat for their human bonus feat (OA normally restricts Rokugani humans to taking an ancestor feat as their human bonus feat). Void Use and its related feats are generally overpowered as well, though a few of them are reasonable. On the plus side, the Rokugan book has some neat Style feats available for warriors of the different Clans, and a feat that allows someone to learn Style feats from another Clan (allowing a gaijin non-Rokugani to learn Style feats from a single Clan, for instance). Some of these feats are also overpowered, but a decent number of them are reasonable. The Rokugan book also has a 20-level Courtier class, a 20-level Inkyo class (enlightened monk, less martial arts focused, more elements and void and miscellaneous-skills focused), and a 20-level Ninja class (pretty much a slightly weaker version of the rogue, with a few different class features, better proficiencies, and d8 hit dice IIRC). That book has a lot of different stuff though, this is pretty much just mentioning some material from the 2nd and/or 3rd chapters, IIRC.