I've only started playing TES beginning with Morrowind. To be honest, I really don't even remember anything about vampires in Morrowind aside from fighting a few as NPC's. I do remember Oblivion though and I gotta say that it all seems completely messed up. The biggest factor for a vampire's strength is time. The longer you spend as a vampire, the stronger you become. I believe lore has it that eventually you become an elder once enough time has passed and it is at this time that your power essentially peaks. It's understandable the need to put a time restraint. If you went into slumber the moment you became a vampire just to become an elder, Skyrim would succumb to its sinister fate. Now Oblivion had it right with the time part (getting stronger as the days past) but had it wrong when those days needed the player not to drink any blood. So if they are to have vampirism in Skyrim (I hope they do) then I would like to see the following....
Sun Light. Sun light is instant death to a vampire. Other than a few cases of half breeds and ancients with immunity (mostly Hollywood hype), the sun will burn to a crisp the skin upon contact. The use of clothes to shield it away is...debatable.
You start off weak and needing to feed. Your stats are not buffed but rather nerfed at this time. Feeding the first time eliminates the debuff, returning your character to normal strength. Each additional day, or night rather, you must feed at least once. As each 24 hour period passes with a successful feeding, you gradually get more powerful. Stats get progressively buffed and you gain vampire powers. This goes until after so many days when you plateau. Now instead of growing in strength, feeding at least once every 24 hours is required to maintain what you have. Failure to do so will cause you to take a step backward. After too many days without feeding, you fall into a dormant state. The game merely counts this state as a death. As for the weakness to sunlight. It's always there, it never changes and it means death if caught in it. For the sake of completing quests, it may be necessary to allow clothing to block out the sun provided a few restrictions are met...
1. The clothing/armor must cover head to toe
2. Only effective during the twilight hours when the sun isn't considered down but the intensity is diminished. This also means that it'll work in mid day provided the weather is bad (heavy overcast, stormy).
Lycanthropy. It was done in Morrowind quite nicely. I don't mean the ring, I mean the disease. I would very much like to see it implemented in Skyrim. As it was.
Open World. This is an open world game there is no doubt about it but a seamless game would be nice. What I mean by that is there not being any loading screens. Certainly not a game stopper if there are but making it seamless would make for better immersion and overall make the game more fluid. It would be nice if you opened a door to a house and it simply swung open like it would going from room to room. It would also be nice if the gates to cities were always open and closed up when the city was under threat. It would be nice if you could enter the city through other means, like flying cause you know there will be flying dragon mount mods. Morrowind did this without a problem, Skyrim should too.
Professions and in game items. Both Morrowind and Oblivion were bad for it. All these bolts of cloth, pieces of ore, black smith and tailoring tools. Among other things. Serving no purpose. It even killed the immersion a bit when you found these items in some of the most unrealistic places. At least food could be eaten raw or used in alchemy. There needs to be professions. Every item should then have a use, and there needs to be a better handle on items in general so you don't find some ridiculous items in places where you should never find it there.
Level Scaling. Level scaling is bad. Plain and simple bad. In Oblivion it really killed. You were restricted on the skills you could pick as primary because if you leveled non combat oriented skills, you couldn't survive a dungeon. Also, when you start out fighting mobs that are pretty easy to kill, then a couple levels later, the same mobs become epic fights, it just killed the game. It really did. I shouldn't have a harder time doing the first fighter guild quest at a higher level than if I were to do it at level 1. I should have an easier time doing it because I am a higher level doing it. If something is too hard to do now, I should be able to do other things, level up a bit, and then come back to it to get it done. I honestly can't think of any good properties behind it. What, it kept you from getting uber powerful gear at the start? Easy, put minimum level and/or skill and/or stat requirements on gear. Though the level of mobs should be set, not scaled and uber powerful items should require you to go places where you'll encounter uber powerful mobs.
Leveling. There needs to be a connection between stat, skill and level. At the start of Oblivion after the king dies, you can go into sneak, plant yourself in a nearby corner and afk your sneak skill to max. All that was required was to put a weight on the walk key or otherwise keep it pressed. If you don't take it as a primary then you are now a level 1 char with max sneak. You are practically invisible. You can then pretty much cruise through the game one shotting everything. One shot didn't do it? That's OK, after your eye icon flickers you are back to sneaking and can hit for another crit. So there needs to be a limiting factor. Like not being able to reach a certain skill level unless stat and/or level criteria are met. Something.
Is it too late? It's never too late because even if it's too late for the initial release, there still can be patches and expansions.