Frankly, Skyrim's melee combat is subpar...you're never going to get anything as weighty and realistic as Dark Souls even with the best mods because it isn't built that way from the ground up. The combat mods mentioned improve things quite a bit, and make combat more strategic and challenging, but you don't want to go in with high expectations.
Mods like Duke Patrick's and Deadly Combat make use of active scripting to constantly check combat states etc. but given how combat can be frenetic, you often don't realise what's happening before it's done, and the lack of visual reactions makes it worse.
Combat mods therefore address these in terms of staggering combatants more, making stamina important (as it should be, Dark Souls-style), and AI changes: enemies are more aggressive and time their attacks, and are more aware of their fellows being taken down. (With DUEL, taking down a bandit in Treva's Watch yesterday summoned nearly all the fellows in the building. Can be fun or plain unfair, depending on your perspective. Companions highly recommended).
FNIS holds some hope: this system allows modders to add new animations to Skyrim without replacing the current ones. If any enterprising modder decides to make new fighting animations for different weapons, it'd be awesome.
Edit: TK HitStop here is a step towards weightier combat.
http://skyrim.nexusmods.com/mods/23681