Hmm...
Features for an original dating sim...
1: Change your hair, buy clothes or even get tattoos (a chibi hero/heroine getting a tattoo makes me laugh), even a beard for males. (For the perverted out there, I'd imagine a hyper expensive "birthday suit" clothing articles to buy would probably score you top marks, even though trying to leave the house with it would get you arrested). Allow people to mix and match different parts of different outfits, and maybe even incorporate these differences in appearance with the various animations found in the game.
2: Choose your gender, with different characters for each.
3: Possibly interactive dates? Rather than sitting whilst your beau to be quizzes you on her favourite colour, actually walk about and do fun things at the locations, and have your date tell you the types of thing she likes doing.
4: Actual reasons to raise your stats. Sure, girls "like" certain stats, but why not enter a beach competition for studliest hunk? Or go on "Who wants to be a sim-ionaire?" to put your intelligence to the test.
5: If you're playing with two genders, why not have the "datables" of one gender be the "friends" of another? Build up a friendship without pursuing sex (for a change), and potentially reap the rewards.
6: Sandbox. Give players the chance to play forever, rather than always rushing to get someone's pants off.
7: Punish infidelity. Or at least make the player give it some thought. Where's girlfriend #1 going to be tonight? In that case, better not go on a date there with girlfriend #2 unless they happen to like sharing.
8: Special items aplenty. Earn yourself enough funds to go to a date in a limo, you're going to understandably impress your potential mate. Turn up decked in the secret wardrobe of biker gear and a Harley, and maybe turn a few heads as you ride off into the sunset with your nerdy boyfriend in tow. A secret time portal for example, could well provide the Sandbox game style previously mentioned.
9: Gifts TO you? Dating games always have you giving gifts to your girl/boy to improve their mood, why not the other way round? Girls can be just as "aggressive" as guys.
10: Secret characters. As well as the previously done secret characters to woo (potentially unlockable over repeat playthroughs), why not secret characters to BE? Tired of being one of the "stock" characters? Unlock Megaman Zero or Samus Aran, or the secret ninja/pirate characters, heck, even a fat Italian plumber and his fruit based girlfriend, or even a few Newgrounds cameos if you can score them. Secret characters could come with set stat beginnings, new wardrobes and purchasables (as well as the standard ones), and of course, new potential love interests, new special items, some real rewards for people playing the game. Unlockables would allow for a much longer game as people can try for more than just to bag all three girls then stop, without the difficulty of trying to implement and create minigames.
Just a few things off the top of my head, feel free to mix and match them, and hopefully you found them at least interesting, if not helpful.