I've been dating quite a few girls and improving my game a lot and I have no problems with kino/escalation. However, girls always tell me they don't feel a spark/connection after 1~2 dates. I'm guessing it's because I'm not really a great talker. I can make jokes about anything, but whenever I talk it's just making conversation, nothing more than that. A 2nd problem is that I become too much of a nice guy and don't make it feel like they have to work to get me while one a date.

Anyone can give me some tips?

Solution is simple - depends on the situation:

1)You build comfort, but you are not attractive(the nice guy).
2)You build attraction, but she is not comfortable(the douchebag in a bad way).

You need to balance this, if you are on a date.

My guess is, that you build a little bit of attraction, a little bit of comfort, she is expecting that you can seduce her, but it ends up with, she thinks you are a loser, and pretty much a useless friend aswell.

I guess you need to be more neutral and instead, try to have some fun. One of the major turn offs, women can spot is, if you are planing your next move and not acting neutral. Do not act like a robot. And yes, never show overwhelming love-feelings, before sex with your date(always remember this, else you destroy the attraction - simple rule).