Haven't played this since it was released on steam, how much has it improved?
I'd say they added about 30+ more hours of game play from Steam release, all new graphics, new animations, lots of new game mechanics, and new characters.
All you gotta do is load up an older version to see the vast number of improvements. I think there's a video somewhere in this thread illustrating that as well. Look at the recent Steam reviews vs the original reviews when the game was released as well, and you'll see the difference, or just pull up some YouTube footage of the new Game Grumps content vs them playing it years ago.
This community often has a frame of mind where if an update doesn't revolve around sex, it's not actually an update, which there has been updates to the sex, but it's not the dev's main focus. The sex has been updated *some*, and though it's better, it's not leaps and bounds beyond what it was, though the new animations are a big improvement over the original. So if that's what you're looking for in terms of "improved", then nah, I wouldn't say you're missing out on anything.
The game is like the old Sierra Leisure Suit Larry games in the sense that you can make a wrong move and die, or get cut off from content, so maybe that's why people are thinking that there's not much more content, but there is actually TONS depending on what choices you make.