Reading the above posts, you might not agree with what I will say, but you ask for my opinion...
I, of course, have my own version of my canon, and I could never swallow KR2000.
The first rule: Knight Rider, the original series, from Season 1 to Season 4, is
canon as it is. (Though when I watch the whole series in a row, I change Voo Doo Knight and Scent of Roses as I feel it to be the right order. I can't really imagine Michael being all funny and joking around after his wife died, or going on missions. I know he went back to the Foundation, but still, I believe he must have needed some time to reignite his own fire.)
Now, everything else for me falls into the partially canon category.
For Knight Rider 2000, Michael's, Devon's and KITT's personalities are canon for me. They are really themselves and I love them. But:
1. I remember how I felt as a kid when I watched Devon die such a meaningless death. I think I decided it in that moment that I will never fully accept this to be true.
2. There are so many plot holes they never explained, like why was KITT just thrown away like that, why didn't anyone do anything about it... it just bugs me.
3. I never understood why they placed it in a "futuristic" year 2000. I think everyone could have already suspected in 1991 that in the year 2000, people won't be cryogenically frozen and shot by stun guns, with chips in their heads. That whole future seemed wrong to me - the original series had its story in the same time it was made, and it was perfect. What was wrong with 1991, with a normal environment? I always liked Knight Rider to be "believable" in the era it was created in, except for some of the sci-fi kind of technology of course, though some of those actually proved to be possible in the 21th century with small computers with huge hard disk and memory capacities, GPS, and so on. Knight Rider 2000 had almost nothing believable about it for me.
4. The red Banshee lookalike... come on, it's a great concept car, but who the hell would go on a to-be-kept-secret operation with a huge red boat on small wheels?
For Knight Rider 2008: too much sex (like, there is Knight Rider and there is porn, but why make them one?), even for me. Of course, I love looking at sexy girls as a more or less grown up man, but when I'm watching Knight Rider, I'm the same kid I was when I first watched the original series. And that kid wants to look at action, a cool guy and a super car, and maybe some bikini girls, yes, but not in that dosage.
Also, the whole storyline started out wrong. I know they had a kind of reboot near the end of the first season where they changed the story to be more like the original series, not saving the world from terrorists Jack Bauer style, but actually helping the innocent and saving ordinary people from criminals above the law, Michael Knight style. It was too late, unfortunately. I could also never accept KARR as a transformer, like it didn't really made sense at all, however I want to put it, it just doesn't work for me.
I loved the series for the characters though, the new KITT, Mike, and the rest. The Mustang was hard to stomach first (could have accepted it more easily if the original KITT were a big freakin Dodge Charger or something, not a sleek, streamlined sports car), but I got used to it. Attack Mode also made sense to me as the modern version of Super Pursuit Mode. I wish the series could have had time to mature and live up to the original one. I'm sure if we've had five or six brilliant seasons, we could have forgot the little errors of the first season. Sadly, it wasn't given justice.
TKR... let's say it had a few good episodes and a few good ideas, but I wouldn't say much else about it. Oh yeah, on second though: KRO was cool.
Well, that's what I believe...
