Archfiends is the 3rd prepainted miniature release from Wizards of the Coast and it gets better every time. The quality of miniatures from WotC's prepainted D&D Miniature line has been improved from their prior two sets, and they're still keeping it affordable at $9.99. The details on some figures are really improving. For instance, Archfiends includes a new common "Warrior Skeleton" that looks better than many skeletons painted by professional miniature painters. "Ragnara, Psychic Warrior" is also a pretty slick looking figure. There is an increase in larger figures from previous sets, including four "Aspects" which are popular D&D villain deities with a midlevel power range (around CR 12) which work well in both D&D and the skirmish game. Finally, the popular Forgotten Realms character Drizzt is now a (rare) figure for the Chaotic Good faction.
I've played a lot more of the Skirmish game that the figures are designed for and I'm surprised how much I like it. The combat cards gives some complex play with relative ease, which is a nice bonus. The new figures add quite a bit to the Skirmish game. The "Gauth" has a dangerous 15 fire damage special ability eye ray, the "Githyanki Fighter" and "Erinyes" have a Dimesion Door ability that was previously only availible to the "Hound Archon" from Harbinger, and Lawful Good finally has a dragon with the nasty "Large Silver Dragon".
The set is not perfect. The humanoid figures are still missing a bit of detail, especially some of the elves -- like the uncommon Mialee, Elf Wizard. I'm a firm believer that figures for PCs should be hand-painted anyway, so in my RPG games any of the short-term NPCs are drawn from these prepainted figures and the long-term PCs are hand painted metal figures.
I'm willing to overlook some of the flaws because they're a relatively inexpensive way to build up a large force of painted figures to help a time-crunched DM. Unfortunately, there are rumors that the price of these figures is increasing, which will cut down on their usefulness. With the increased price of Giants of Legend to $19.99 (for 8 figures and 1 huge figure) and I suspect future sets will be around $12.99, I think this is the last easily affordable set.