The original game was nothing special - basically very generic eroge stuff, with none of the emotional drama that made previous Key games amazing. This anime has basically the same feel, without dragging on for far too long like eroge do, so it could be argued to be an improvement. On the other hand, some of the voice acting in the game was superb (Saigusa!), but is crap in the anime - so it pretty much breaks even.
In other words: So far, so mediocre. I'll definitely keep watching it though to see how it develops, since I didn't have enough interest to play more than a couple of routes in the game.
EDIT: Actually, what annoys me about Saigusa in the anime, more than the voice acting, is that she just comes across as being an annoying retarded idiot, as opposed to being deliberately funny.