Morrowind, hardest game for vampires?

[MidbossVyers]

Arena: No playable vampires (or werewolves, or guilds)
Daggerfall: Vampires suffer from sun damage. People will still talk to them?
Morrowind: Vampires suffer from sun damage. Most people, including those tied with the main quest, will not talk with them, but do Back Path.
Oblivion: Vampires suffer from sun damage if not feeding properly. Most people, including those tied with the main quest, will not talk with them, if blood-starved. Feeding rectifies issue.
Skyrim: Vampires suffer non-lethal solar debilitation. Most people, including those tied with the main quest, will not talk with them, if blood-starved. Feeding rectifies issue.

You couldn't do much in Arena, so whatever, In Daggerfall, vampires do suffer sun damage, but from what I read and from what little I played, there is little issue with speaking with quest givers (though, from a role-playing perspective, you might end up aligning yourself with the Underking or Mannimarco, anyway). In Morrowind, not only do vampires suffer sun damage, the only way that they can complete the main quest is by doing the Back Path, which permanently weakens your health by 200 to 225 points. In Oblivion, feeding regularly pretty much negates all previous disadvantages quest-wise. In Skyrim, being a vampire does not affect the main quest line at all, with Dawnguard installed. Coincidentally, Morrowind is the only province/kingdom where necromancy is de jure (totally using real-life legal terms in a fantasy setting) illegal, rather than just de facto or not illegal at all. What's with the undead hate in Morrowind?

[legoless]

What's with the undead hate in Morrowind?

You just answered your own question. It's illegal there because the Dunmer are ancestor worshippers. Anything other than the traditional binding of ancestral spirits is the highest level of profanity. Imperial culture has a soft spot for vampires, while in Morrowind the Temple launches regular crusades on their lairs and actually wiped them out on Vvardenfell for a long time before the events of Morrowind.

[MidbossVyers]

I also noted that, while the Vigilants of Stendarr hunt vampires among others, doing the vampire quests in Daggerfall actually increased your reputation with the followers of Stendarr and Julianos, while decreasing your reputation with the followers of the other Divines, except for Kynareth (Talos apparently wasn't a thing back then), http://uesp.net/wiki/Daggerfall:Deadly_Knowledge although Julianos does make sense because God of Wisdom, Vampiric wisdom of the ages, etc.

[legoless]

The Vigilants of Stendarr are a Fourth Era phenomenon. The Oblivion Crisis resulted in a lot of cultural change.

[MidbossVyers]

Ironically, despite having negative affinity with vampires in Daggerfall, the Mages Guild is one of the few guilds that vampires can join in Morrowind.