Dynasty Warriors 5 has the most characters than any other game in the series, overall there are over fourty playable characters, each with their own musou mode. In Dynasty Warriors 4, a lot of characters from Dynasty Warriors 3 were taken out, but were reintroduced in Dynasty Warriors 5 with complete makeovers. However, in Dynasty Warriors 6, eight characters were taken out that were in Dynasty Warriors 5, and you could only play musou mode with a few characters, but the creators tried to make up for it with special graphics. Even so, Dynasty Warriors 5 is the most popular game in the entire series. It was actually the breakthrough in the series since it added more items, better graphics, new stages, new senerios, new characters, redone characters, and easier gameplay.
It was also after Dynasty Warriors 5 was created, that Koei made Warriors Orochi 2, which mixed together the characters and designs of Dynasty Warriors 5 and Samurai Warriors 2. So if there's ever a Warriors Orochi 3, they'll probably mix together the designs of the characters of Dynasty Warriors 6.