I like armor that is in some way plausible and fits the setting.
Historically inspired is cool, and there are tons of historical styles that look awesome but haven't been used in RPGs much/at all. Late ancient Persian cataphracts with their scale armor and lamellar greaves and bracers look fucking badass. Those viking helmets with the face guard are awesome. Renaissance full plate armor or 17th century cuirassier breastplates are dope. And it is a crime that the Mycenean Dendra panoply (aka lobster cuirass) has never been implemented in a game, it's so cool it even looks like a fantasy armor.
Also, some impractical armors can easily be made plausible by having them be a cultural thing or a sign of rank. Some Roman officers wore cool iron face masks which had more of a psychological function (looks scary) than pure protection. Roman officers wore muscle cuirass plate armor, which was shaped in the form of a sculpted torso, because it looks fancy and cool, not for any practical reason. It also stands out, which is important for an officer so your own men know you're the boss guy. In the same vein, boobplate for female characters can be made plausible: it's impractical, yes, but nobody cares because it's more of a rank signifier and a prestige object than a purely practical suit of armor. Even chainmail bikinis and half-naked barbarians can be explained plausibly as a cultural thing: the Celts had warriors who fought naked - no, not just bare-chested, entirely naked, with their dong swinging to and fro as they charge at you - because they believed armor was for cowards, and the gods would protect them better than any layer of clothing and armor.
Of course, that all requires armor (and weapons, too) to have a purpose in the game world beyond "this gives +X defense when you equip it". Armor as a cultural and/or rank thing. Morrowind did this quite well: the fancy Ordinator armor with its impractical but cool full-face helmet is worn only by ordinators, a symbol of their office. If you wore any piece of Ordinator armor and talked to an Ordinator, he'd attack you for it, because you're not allowed to wear this armor as a non-Ordinator. That's cool. When you join the Imperial Legion, you have to wear an Imperial Legion chest armor piece or other legion members won't talk to you ("Where's your uniform, legionary?"). And some factions had clear preferences in which armor they wore: if you meet a guard wearing bonemold armor, he probably belongs to house Redoran. That makes armor more than just a piece of equipment with defensive stats. Morrowind's armor was a part of the worldbuilding, people of certain factions preferred certain armor, some armor was an insignium of rank, etc etc. Characters weren't just equipped with different armor parts willy nilly. The world designers actually put some thought into which NPCs would wear which kind of armor. Morrowind's armor is also not as obviously tiered as Oblivion's and Skyrim's. Each armor group has some redundant pieces that are roughly equal in their protection value. Netch leather vs nordic fur vs chitin armor for example: the difference isn't that major, but the different armors exist because they have a cultural reason for existing.
I'm also a big fan of Morrowind and KCD style layered armor/clothing systems. It's much cooler than the simple system of having full armor suits count as single items, because it allows you to mix and match (which was done very regularly in history, especially among irregular troops who supplied their own armor rather than being issued standard uniforms by the army). You can put a plate cuirass over chainmail, for example, and you have a lot more loot to hunt down if armor is split into parts, which makes exploration more rewarding. Hunting down a full daedric armor set in Morrowind is great because it's such a rare armor (most pieces exist only once or twice in the entire gameworld). Partial armor is more realistic in many aspects, and allows for the recreation of many historical armor styles. Roman legions at most points in history would only wear one greave, for example (on the forward-facing leg), for weight reduction and equipment cost reduction.
I don't need armor to be fully historical, but I like it to be believable and look interesting. Morrowind did a great job there, its designs stayed mostly believable, it used specific materials of the gameworld (glass, ebony, chitin, netch leather), and it had cultural significance. It had style and identity. Meanwhile WoW style cartoony HUEG PAULDRONS armor design just looks boring and lacks identity. It also looks ridiculous and impractical most of the time.
I'd like to see more of the less popular historical armor styles in RPGs: give us some scale mail and lamellar armor instead of only chainmail and plate all the time! I'd also like to see the return of the glorious chainmail bikini because it's sexy
AND it can make sense within the context of the setting (a badass warrioress wearing a chainmail bikini on purpose as something that doesn't offer much protection, because she trusts in her own ability and the protection of the gods and doesn't need any better armor; half-naked barbarians work just as well for the same reasons).
Finally, a nice mix of historical armors and fantasy armors that look cool and that I'd like to see more of in RPGs:
EDIT: Oh, yeah, also mythology had much, much cooler armor designs than any fantasy RPG:
Agamemnon equipped with a Cypriote cuirass made of overlapped scales on which, divided in the different zones of the armour, there are ten rows of black enameled, twelve of gold and 20 of tin; furthermore a bronze belt decorated with silver motif; neck guard with snakes in "rainbow" color; beautiful greaves reinforced with silver ankle protections, sword with gold nails and silver scabbard, can also be assumed.
The large shield and the elaborated helmets with crests, tubes, and horse plume are fully described in the pages dedicated to the Iliad shields and the Iliad helmets.