The Xtreme Legends games ARE expansion packs - they can be played stand-alone, but you get the full benefit from them if you own the original game as well. The DW8 complete edition contains both the original game & Xtreme Legends expansion built into one, you get the full options & benefits from both. Dynasty Warriors 3 was the first to have an Xtreme Legends expansion, and every DW game since then has had one EXCEPT for DW6.
Dynasty Warriors: Empires games have a somewhat more tactical side. The battles themselves are pretty much the same, but in-between battles you have options to ally with or against other nations, move troops, invade, etc. These are fully stand-alone games and do not require or benefit from owning their numbered counterparts at all. Dynasty Warriors 4 was the first to get an Empires counterpart, and all DW games since then have had one.
There are 2 Dynasty Tactics games on the PS2, these are even more tactical in nature.
Then there are the spin-offs, the main two being Samurai Warriors (which is set in Japan, as the name implies) and Warriors Orochi (which is a combination of Dynasty & Samurai Warriors w/ supernatural enemies mixed in. There are lots more, just let me know if you want to hear about them all.
