Initial D is definitely on the top of my list of favorite animes, probably even surpassing Rurouni Kenshin.
For one, the show actually makes sense. It has way more realism than all the Fast and the Furious movies combined, and I like that it operates under the premise that it's more about technique than power. And tacky as it seems, I actually like the fact that Takumi remains undefeated. I hate animes wherein the main character always starts off as a pushover (which is why I also like RK, and why I hate Naruto and everything like it).
But I think that the best part about the show is that it actually gets you excited. Maybe it's just me, but I get all giddy whenever Takumi does his thing. Best moment of the show for me was the blind attack on the pro driver in the 4th Stage - the timing, the music, the dialogue, and the overall feel just makes it a very involving thing to watch.
What I like about the 5th Stage is the much improved graphics. It's a bit weird though that the characters barely look like their 1st-4th Stage counterparts, but I'll get used to it. What bothers me is that they seem to have forced Takumi to have a love life. The entry of Mika seemed too tacky, but then again, the romance takes a backseat to the racing so it's fine.