The visual novel is as good as the anime, if not better due to certain scenes going on longer in the visual novel that where short in the anime (example: Remember that talk with Sunohara about tea just before the first Illusionary World scene? Yeah, there's a lot more to that part... And it's comedy gold).
Also, there is a character that was completely cut from the anime in the visual novel, a very feminine guy whose name escapes me at the moment. Likely cut just because Sunohara genuinely thinks he is a she and pursues what Tomoya calls "Unrequited Love." (Remember that bit about comedy gold?)
And as
>>2 said, this game is looooooooooooooooooooooooooooong. Like, "You Will Play Me For Many Moons" long, but not really like "This game drags on" long. It feels really different than the anime to play, too, so while you know some of the things that will happen, you'll still get a lot of new things as you go.
... Did I mention I love Clannad? Should be obvious by now, really XD
