I visited the Artcaffe locations at the Westgate Mall as well as the Village Market Mall recently. I give them an overall very good rating mostly because they are somewhat of an oasis in a town where there are not too many comfort zones outside the luxury hotels. They are great for a cup of coffee with the morning papers (the coffee was fine). The pastries are not bad at all (the cinnamon role didn't give me heartburn...) and the food offerings are more than acceptable. I didn't run into any problems concerning hygiene or spoiled food. All in all I find the atmosphere welcoming and the service level reasonable for an often crowded venue. I guess that if you are really in a hurry, the service might at times seem slow or distracted, although I didn't get that feeling. My experience is that this is probably par for the course in many Nairobi cafes.
To sum it up, don't go there for a gourmet experience. I doubt that even they make that claim. But it is an inviting, safe and positive place to while away some time, to work on your computer (free wifi!) and to people watch.
As at many similar places in upscale settings in Nairobi, the preponderance of customers are expatriates and foreigners of one ilk or another - all being served by locals. Those are still the unfortunate facts of life. Since I don't think that I can change that singlehandedly, I will be going back to the Artcaffes whenever I visit Nairobi.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.