I just wanted to re-post this link to a mostly spoiler free review, which was written early in 2018.
https://www.animenewsnetwork.com/shelf-life/2018-01-22/.126717#clannad
My first experience was the VN but I bought and watched the anime quite soon afterwards and I was really pleased that it upheld my high opinion of the work, some parts enhanced by animation and most of the changes or omissions are not too critical.
The one drawback is that it is harder for a viewer who has not played the VN to realise the full significance of the light orbs in the resolution of the story - although saying that there are plenty of clues there for those who pay close attention. Nonetheless as the review says it can be a bit divisive. For the most part though the most emotional scenes retain their impact and I really felt the heartbreak of moments such as {major spoilers for Clannad and After Story} Kotomi’s breakdown and Nagisa’s death and the emotional high of {After Story spoiler}
Ushio’s sunflower field scene even more in the anime.
In general turning the multiple routes into a linear story was successful, the 4 OVAs/Extras are not really essential viewing as far as the main story arc is concerned and probably the weakest parts. It has some flaws and curious creative choices, e.g. the way it adapts Tomoyo’s route, for sure but nothing too major. Pacing can be a little uneven and feel slow at times, but the comedy moments are generally well played out.
For anyone who can’t spare the time to play through 100 hours or of the VN the anime does offer a pretty good alternative and even if you’ve seen the VN it really is worth considering the anime box sets too.